This was a lot harder than I originally thought!  :)
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3957 words with four letters
http://www.a2zwordfinder.com/cgi-bin/scrabble.cgi?Letters=&Pattern=____&MatchType=Exactly&MinLetters=4&SortBy=Alpha&SearchType=Scrabble

I counted 174 Four letter regular verbs
http://www.englishclub.com/vocabulary/regular-verbs-list.htm

I counted 3 Four letter irregular verbs
http://www.englishclub.com/vocabulary/irregular-verbs.htm
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994 words with three letters
http://www.a2zwordfinder.com/cgi-bin/scrabble.cgi?Letters=&Pattern=____&MatchType=Exactly&MinLetters=3&SortBy=Alpha&SearchType=Scrabble

I counted 48 Three letter Regular Verbs

http://www.englishclub.com/vocabulary/regular-verbs-list.htm

I counted 2 Three letter irregular verb

http://www.englishclub.com/vocabulary/irregular-verbs.htm
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99 words with two letters
http://www.a2zwordfinder.com/cgi-bin/scrabble.cgi?Letters=&Pattern=____&MatchType=Exactly&MinLetters=2&SortBy=Alpha&SearchType=Scrabble

There are no two letter verbs.
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2 words with one letter.
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I can't possibly do nouns as there are billions upon billions of people, places and things in the English language.

2? one letter words
101 two letter words
873 three letter words
3957 four letter words

2 letter list: http://www.trussel.com/scrabble/2words.htm

3 letter list: http://www.msoworld.com/mindzine/news/proprietary/scrabble/features/all3s.html

4 letter list: http://www.a2zwordfinder.com/cgi-bin/scrabble.cgi?Letters=&Pattern=____&MatchType=Exactly&MinLetters=4&SortBy=Alpha&SearchType=Scrabble

and yes for the one letter words, that is a guess that it is "a" and "I". I could not find an actual number for one letter words anywhere. So assuming no words have been added or taken out of the language since those numbers were posted, the total should be 4933 words.

Hope this helps.

It seems that the question of how many words has been answered already, but the number of possible permutations of letters may also help you.

We use permutation instead of combinations because the case "abcd" is distinct from the case "dcba".

There are 26 letters in the alphabet, so 26 P 4 permutations are possible. (This is evaluated using the formula n P r = n! / (n-r)!)

358800 four letter permutations

26 P 3 = 15600 three letter permutations

26 P 2 = 650 two letter permutations

26 P 1 = 26 one letter permutations total = 375076 possibilities

There is an interesting study on this, "The Change in the Number of Four-letter Words in the English Language" which is about 10 years old, yet it still seems to work, the mathematical equations they came up with to calculate the number of words have not changed.
It's very hard to break these up into nouns, verbs, etc. 
In order to estimate the total number of four-letter words in each dictionary
(Mˆ ), it is necessary to find the estimated number of four-letter words per page (m), and the estimated density of four-letter words per page (λˆ).
The following equations were used to calculate these values where n is the
number of pages sampled.

The estimated number of four-letter words in the 1950 dictionary is
approximately 4,929 and 6,974 for the 1986 dictionary. To get a better idea of possible values for the true number of four-letter words in each dictionary, a confidence interval must be constructed to determine the range in which the true number of four-letter words lies.

See list bellow, 4 letter english words, for detail visit the website http://www.wordbyletter.com/words_by_length.php

Total : 4051 words (approximatelly)

4 letter words starting with "A"

aahs, abay, abba, abbe, abbr, abed, abet, abib, abid, abit,
able, ably, abox, abra, abut, abye, acct, aced, aces, ache, achy, acid, aclu,
acme, acne, acre, acts, acyl, adam, adar, adaw, adds, adit, ados, adry, advt,
adze, aeon, aero, aery, afar, afer, affy, afro, agar, aged, agen, ages, agha,
agin, agio, agni, agog, agon, agre, ague, ahem, ahey, ahoy, aide, aids, aiel,
ails, aims, aino, airs, airy, ajar, ajog, akin, alae, alai, alan, alar, alas,
alba, albe, albs, alco, alee, alem, ales, alew, alfa, alga, alii, alit, alls,
ally, alma, alme, alms, aloe, alow, alps, also, alto, alum, amah, ambo, amel,
amen, amex, amia, amic, amid, amir, amis, amit, amma, ammo, amok, amps, amts,
amyl, anal, anan, anas, ands, anes, anet, anew, anil, anis, ankh, anna, anne,
anno, anoa, anon, ansa, ansi, anta, ante, anti, ants, anus, apar, aped, aper,
apes, apex, apis, apod, apse, apus, aqua, arab, arak, arch, arco, arcs, area,
ares, aret, arew, argo, aria, arid, aril, arks, arms, army, arna, arow, arse,
arts, arty, arum, asap, asci, asea, ashy, asia, asks, asps, asse, assn, asst,
atma, atmo, atom, atop, atte, attn, atty, atwo, aube, auks, auld, auln, aune,
aunt, aura, auto, avdp, avel, aver, aves, avid, avie, avis, avow, away, awed,
awes, awls, awns, awny, awol, awry, axal, axed, axel, axes, axil, axis, axle,
axon, ayah, ayen, ayes, ayle, ayme, ayry, azym,

4 letter words starting with "B"

baal, baas, baba, babe, babu, baby, bace, bach, back, bade,
bads, baff, baft, bags, baht, bail, bain, bait, bake, bald, bale, bali, balk,
ball, balm, banc, band, bane, bang, bank, bans, barb, bard, bare, barf, bark,
barm, barn, bars, base, bash, bask, bass, bast, bate, bath, bats, batz, baud,
bauk, bawd, bawl, bawn, baya, bays, bdrm, bead, beak, beal, beam, bean, bear,
beat, beau, beck, bede, beds, beef, beem, been, beep, beer, bees, beet, bega,
begs, behn, belk, bell, belt, bema, bend, bene, bens, bent, bere, berg, berm,
bess, best, beta, bete, bets, bevy, beys, bias, bibb, bibs, bice, bide, bids,
bier, biff, biga, bigg, bike, bikh, bile, bilk, bill, bind, bine, bing, bink,
bins, biol, bion, bios, bird, birk, birl, birr, birt, bise, bish, bisk, bite,
bito, bits, bitt, blab, blae, blah, blat, blay, bldg, blea, bleb, bled, blee,
blek, blet, blew, blin, blip, blob, bloc, blot, blow, blub, blue, blur, blvd,
boar, boas, boat, bobs, boca, boce, bock, bode, bods, body, boer, boes, boff,
bogs, bogy, boil, boke, bola, bold, bole, boll, boln, bolo, bolt, bomb, bona,
bond, bone, bong, bono, bons, bony, boob, book, boom, boon, boor, boos, boot,
bops, bord, bore, born, bort, bosa, bosh, bosk, boss, bote, both, bots, boud,
bouk, boul, boun, bour, bout, bowl, bows, boxy, boyo, boys, boza, bozo, brad,
brae, brag, bran, bras, brat, braw, bray, bred, bren, bret, brew, brid, brie,
brig, brim, brin, brio, brit, brob, brog, bros, brow, bruh, brun, brut, buat,
bubo, bubs, buck, buds, buff, bufo, bugs, buhl, bulb, bulk, bull, bump, bums,
bund, bung, bunk, bunn, buns, bunt, buoy, burg, burh, burl, burn, burp, burr,
burs, burt, bury, bush, busk, buss, bust, busy, buts, butt, buys, buzz, byes,
byre, byss, byte,

4 letter words starting with "C"

caas, cabs, cack, cade, cadi, cads, cady, cafe, cage, cagy,
cake, caky, calc, calf, cali, calk, call, calm, calx, came, camp, cams, cand,
cane, cans, cant, cany, cape, caps, card, care, carf, cark, carl, carp, cars,
cart, casa, case, cash, cask, cass, cast, cata, cate, cats, cauf, cauk, caul,
cave, cavy, cawk, caws, cayo, cays, ceca, cede, cees, ceil, cell, celt, cent,
cere, cero, cert, cess, cest, cete, chab, chad, chak, cham, chap, char, chat,
chaw, chef, chem, ches, chew, chez, chia, chic, chid, chin, chip, chit, chop,
chou, chow, chub, chud, chug, chum, ciao, cill, cima, cine, cion, circ, cist,
cite, city, cive, cize, clad, clam, clan, clap, claw, clay, clee, clef, cleg,
clem, clew, clio, clip, clod, clog, clop, clot, cloy, club, clue, clum, cmdg,
coag, coak, coal, coat, coax, cobs, coca, cock, coco, coda, code, cods, coed,
cogs, coho, coif, coil, coin, coir, coit, coke, cola, cold, cole, coll, colp,
colt, coly, coma, comb, come, comp, cond, cone, conf, cong, conj, conk, conn,
cons, cont, cony, cook, cool, coom, coon, coop, coos, coot, cope, cops, copy,
cora, corb, cord, core, corf, cork, corm, corn, corp, cosh, coss, cost, cosy,
cote, cots, coup, cove, cowl, cows, coxa, cozy, crab, crag, cram, cran, crap,
craw, cray, cree, crew, crib, cric, crop, crow, crud, crup, crus, crut, crux,
ctrl, cuba, cube, cubs, cuca, cuds, cued, cues, cuff, cuke, cull, culm, cult,
cund, cunt, cups, curb, curd, cure, curl, curr, curs, curt, cusk, cusp, cuss,
cute, cuts, cyan, cyma, cyme, cyon, cyst, czar,

4 letter words starting with "D"

dabb, dabs, dace, dada, dade, dado, dads, daff, daft, dago,
dais, dale, dalf, dame, damn, damp, dams, dana, dane, dang, dank, dare, darg,
dark, darn, darr, dart, dase, dash, data, date, daub, dauk, daun, dauw, dave,
dawe, dawk, dawn, days, daze, dbms, dead, deaf, deal, dean, dear, deas, debs,
debt, deck, deco, dede, deed, deem, deep, deer, dees, deev, deft, defy, degu,
deil, deis, deja, dele, delf, deli, dell, deme, demi, demo, demy, dens, dent,
deny, dept, dere, derf, derk, derm, dern, desk, dess, deus, deux, deva, deve,
devi, dews, dewy, deye, deys, dhow, diag, dial, diam, dian, dias, dibs, dice,
dich, dick, dict, dido, didy, died, diem, dies, diet, digs, dika, dike, dill,
dime, dims, dine, ding, dink, dins, dint, dips, dipt, dire, dirk, dirl, dirt,
disc, dish, disk, dite, ditt, diva, dive, dizz, djin, doab, doat, dock, docs,
dodd, dodo, doer, does, doff, doge, dogs, dogy, doit, dojo, doko, dole, dolf,
doll, dolt, dome, doms, dona, done, dong, doni, dons, doom, doop, door, dope,
dopy, dorm, dorn, dorp, dorr, dors, dory, dose, doss, dost, dote, doth, dots,
doty, douc, dour, dout, dove, dowl, down, dows, doxy, doze, dozy, drab, drad,
drag, dram, drat, draw, dray, dree, dreg, drek, drew, drey, drib, drie, drip,
droh, drop, drow, drub, drug, drum, drys, duad, dual, duan, dubb, dubs, duce,
duck, duct, dude, duds, duel, dues, duet, duff, dugs, duke, dull, duly, dumb,
dump, dune, dung, dunk, duns, dunt, duos, dupe, dura, dure, durn, duse, dusk,
dust, duty, dyad, dyas, dyed, dyer, dyes, dyke, dyne,

 

4 letter words starting with "E"

each, eale, eame, earl, earn, ears, ease, east, easy, eath,
eats, eaux, eave, ebbs, ebon, eccl, eche, echo, ecol, econ, ecru, ecus, edam,
edda, eddy, eden, edge, edgy, edit, eeke, eels, eely, eery, effs, efts, egad,
egal, eger, eggs, egis, egos, egre, eigh, eild, eire, ejoo, eked, ekes, elan,
elds, elhi, elix, elke, elks, ells, elms, elmy, else, elul, elve, emeu, emew,
emir, emit, emmy, emus, emyd, encl, ends, engr, enow, envy, eons, epee, epen,
epha, epic, epos, eras, erat, ergo, ergs, eric, erie, erin, erke, erme, erne,
erns, eros, errs, erse, ersh, erst, eses, esox, espy, esse, etch, ethe, etna,
etui, etym, euge, eugh, eval, even, ever, eves, evet, evil, ewer, ewes, ewry,
exam, exec, exes, exit, exon, expo, eyas, eyed, eyen, eyer, eyes, eyet, eyle,
eyne, eyot, eyra, eyre, eyry,

 

4 letter words starting with "F"

face, fact, fade, fads, fady, fags, fail, fain, fair, fait,
fake, falk, fall, falx, fame, fand, fane, fang, fans, fard, fare, farl, farm,
faro, fart, fash, fast, fate, fats, faun, faut, faux, fawe, fawn, fays, faze,
feal, fear, feat, feck, feds, feed, feel, fees, feet, fehm, fele, fell, felt,
feme, fend, fens, feod, fere, ferm, fern, fers, fess, fest, feta, fete, feud,
fiar, fiat, fibs, fica, fice, fico, fide, fido, fids, fief, fife, figs, fiji,
fike, file, fill, film, fils, find, fine, fink, finn, fins, fint, fire, firk,
firm, firs, fisc, fish, fisk, fist, fits, fitt, fitz, five, fixe, fizz, flab,
flag, flak, flam, flan, flap, flat, flaw, flax, flay, flea, fled, flee, flet,
flew, flex, flip, flit, flix, floe, flog, flon, flop, flow, flub, flue, flus,
flux, foal, foam, fobs, foci, foes, foge, fogs, fogy, foil, foin, fold, folk,
fond, fone, font, food, fool, foot, fops, fora, ford, fore, fork, form, fort,
foul, four, fowl, foxy, fozy, frab, frag, frap, frat, frau, fray, fred, free,
fren, fret, frig, frim, frit, friz, froe, frog, from, frow, frug, fuar, fubs,
fuci, fuck, fuds, fuel, fuff, fuga, fugh, fugs, fuji, full, fume, fumy, fund,
funk, furl, furs, fury, fuse, fuss, fust, fuze, fuzz, fyke, fyrd,

 

4 letter words starting with "G"

gabs, gaby, gade, gads, gael, gaff, gaga, gage, gags, gain,
gait, gala, gale, gall, gals, galt, game, gamp, gams, gamy, gane, gang, gaol,
gape, gaps, gapy, garb, gard, gare, gars, gary, gash, gasp, gast, gate, gats,
gaud, gaul, gaur, gave, gawk, gawn, gays, gaze, geal, gean, gear, geat, geck,
gedd, geed, geek, geer, gees, geet, geez, geic, gein, geld, gels, gelt, gems,
gena, gene, gens, gent, genu, geog, geol, geom, gere, germ, gern, gery, gest,
geth, gets, geum, ghat, ghee, gibe, gibs, gide, gift, gigs, gila, gild, gile,
gill, gilt, gimp, ging, ginn, gins, gips, gird, gire, girl, girn, girt, gise,
gist, gite, gith, give, glad, glee, gleg, glen, glew, gley, glib, glim, glob,
glom, glop, glow, glue, glum, glut, glyn, gnar, gnat, gnaw, gnew, gnof, gnow,
gnus, goad, goaf, goal, goar, goat, gobs, goby, gode, gods, goel, goen, goer,
goes, goff, gogo, gold, golf, goll, gome, gone, gong, good, goof, gook, goon,
goop, goos, goot, gord, gore, gorm, gory, gosh, goss, gote, goth, goud, gour,
gout, gove, govt, gowd, gowk, gowl, gown, goys, grab, grad, graf, gram, gras,
gray, gree, gres, gret, grew, grey, grid, grig, gril, grim, grin, grip, gris,
grit, grog, gros, grot, grow, grub, gruf, grum, guam, guan, guar, guck, guff,
guhr, guib, guid, gula, gule, gulf, gull, gulp, gult, guly, gump, gums, guna,
gung, gunk, guns, gurl, gurt, guru, gush, gust, guts, guys, guze, gybe, gyle,
gyms, gyps, gyre, gyri, gyro, gyse, gyte, gyve,

 

4 letter words starting with "H"

haaf, haak, haar, hack, hade, hadj, haft, hags, hahs, haik,
hail, hair, haji, hajj, hake, hale, half, halk, hall, halm, halo, halp, hals,
halt, hame, hams, hand, hang, hank, haps, hard, hare, hark, harl, harm, harp,
hart, hary, hase, hash, hask, hasp, hast, hate, hath, hats, haul, haum, haut,
have, hawk, hawm, haws, haye, hays, haze, hazy, head, heal, heam, heap, hear,
heat, hebe, heck, heed, heel, heep, heer, heft, heil, heir, held, hele, hell,
helm, help, heme, hemp, hems, heng, hens, hent, herb, herd, here, herl, hern,
hero, herr, hers, hert, hery, hesp, hest, hete, heuk, hewe, hewn, hews, hexa,
heyh, hick, hide, hied, hies, high, hike, hile, hill, hilt, hind, hine, hink,
hint, hipe, hips, hire, hirs, hisn, hiss, hist, hits, hive, hizz, hoar, hoax,
hobo, hobs, hock, hods, hoed, hoer, hoes, hogh, hogo, hogs, hoit, hoke, hold,
hole, holm, holp, holt, holy, home, homo, homy, hond, hone, hong, honk, hont,
hood, hoof, hook, hool, hoom, hoop, hoot, hope, hopi, hops, hora, hore, horn,
hors, hose, hosp, host, hote, hots, houp, hour, hove, howe, howl, howp, hows,
hubs, huch, huck, hued, huer, hues, huff, huge, hugs, hugy, huke, hula, hulk,
hull, hump, hums, hung, hunk, huns, hunt, hurl, hurr, hurt, hush, husk, huso,
huts, huzz, hyde, hyen, hyke, hymn, hyne, hype, hypo,

 

4 letter words starting with "I"

iamb, ibex, ibid, ibis, icbm, iced, ices, icky, icon, idea,
idee, idem, ideo, ides, idle, idly, idol, idyl, ieee, iffy, ihvh, ikon, ilex,
ilia, ilke, ilks, ills, illy, imam, iman, impi, imps, inca, ince, inch, inde,
inee, info, inia, inks, inky, inly, inne, inns, inro, inst, intl, into, intr,
ions, iota, iowa, ipso, iran, iraq, ired, ires, iris, irks, iron, irpe, isis,
isle, isms, ital, itch, item, iter, iuds, iwis, ixia, izar,

 

4 letter words starting with "J"

jabs, jack, jade, jagg, jags, jail, jain, jake, jako, jamb,
jams, jane, jant, jape, jarl, jars, jasp, jato, java, jawn, jaws, jawy, jays,
jazz, jean, jeat, jeel, jeep, jeer, jeez, jefe, jehu, jell, jerk, jess, jest,
jesu, jets, jeux, jews, jibb, jibe, jibs, jiff, jigs, jill, jilt, jimp, jink,
jinn, jins, jinx, jive, jobs, jock, joes, joey, jogs, john, joie, join, joke,
jole, joll, jolt, jose, josh, joso, joss, jota, jots, jouk, joul, jour, jove,
jowl, joys, juan, juba, jube, judo, judy, juga, juge, jugs, juju, juke, juli,
july, jump, june, junk, juno, jupe, jura, jure, jury, just, jute, juts,

 

4 letter words starting with "K"

kadi, kage, kagu, kail, kain, kaka, kale, kali, kama, kame,
kami, kand, karn, kart, kate, kava, kawn, kayo, kays, keck, keel, keen, keep,
kegs, keir, keld, kele, kell, kelp, kelt, kemb, kemp, keno, kens, kent, kepi,
kept, kerb, kerf, kerl, kern, kers, kess, kest, keta, keys, khan, kibe, kiby,
kick, kids, kier, kiev, kike, kill, kiln, kilo, kilt, kind, kine, king, kink,
kino, kins, kipe, kips, kirk, kish, kiss, kist, kite, kith, kits, kiva, kive,
kiwi, knab, knag, knap, knar, knaw, knee, knew, knit, knob, knop, knor, knot,
know, knox, knur, koan, koba, koel, koff, kohl, kola, kong, kook, koto, kris,
ksar, kuda, kudo, kudu, kung, kurd, kwhr, kyar, kyat, kyaw, kyke,

 

4 letter words starting with "L"

laas, labs, lace, lack, lacy, lade, lads, lady, laft, lags,
laic, laid, lain, lair, lait, lake, lakh, laky, lalo, lama, lamb, lame, lamm,
lamp, lams, land, lane, lang, lank, lant, laos, lapp, laps, lard, lare, lark,
lars, lary, lash, lask, lass, last, lata, late, lath, laud, laus, lava, lave,
lawe, lawm, lawn, laws, lays, laze, lazy, lead, leaf, leak, leal, leam, lean,
leap, lear, leas, leat, lech, lect, leed, leef, leek, leep, leer, lees, leet,
left, lege, legs, leis, leks, leme, lena, lend, lene, leno, lens, lent, leod,
leon, leos, lere, lese, less, lest, lete, lets, leva, leve, levi, levo, levy, lewd,
leys, liar, lias, libs, lice, lich, lick, lido, lids, lied, lief, lien, lier,
lies, lieu, life, lift, lige, like, lill, lilt, lily, lima, limb, lime, limn,
limo, limp, limu, limy, lind, line, ling, link, lino, lins, lint, liny, lion,
lips, lira, lire, lisp, liss, list, lite, lith, lits, live, lixt, liza, load,
loaf, loam, loan, lobe, lobo, lobs, loca, loch, loci, lock, loco, lode, loft,
loge, logo, logs, logy, loin, loir, loke, loki, loll, loma, lond, lone, long,
loob, loof, look, lool, loom, loon, loop, loos, loot, lope, lops, lord, lore,
lori, lorn, lory, lose, loss, lost, lote, loth, loto, lots, loud, louk, loup,
lour, lout, love, lowh, lowk, lown, lows, luau, lube, luce, luck, lucy, lues,
luff, luge, lugs, luke, lull, lulu, lump, luna, lune, lung, lunk, lunt, luny,
lure, lurg, lurk, lush, lusk, lust, lute, luth, luxe, lyam, lyes, lyne, lynx,
lyra, lyre,

4 letter words starting with "M"

maad, maat, mace, mach, mack, macs, made, mads, mage, magi,
mags, maha, maia, maid, mail, maim, main, make, maki, mala, male, mali, mall,
malm, malt, mama, mand, mane, mano, mans, manu, manx, many, maps, mara, marc,
mare, mark, marl, mars, mart, marx, mary, mase, mash, mask, mass, mast, mate,
math, mats, matt, maty, maud, maul, maut, mawk, maws, maxi, maya, mayo, mays,
maze, mazy, mead, meak, meal, mean, mear, meas, meat, meaw, mech, mede, meed,
meek, meer, meet, mega, mein, meld, mell, melt, memo, mend, mens, ment, menu,
meow, merd, mere, merk, merl, mero, mesa, mesh, mess, mest, meta, mete, meth,
meum, meve, mewl, mews, mias, mibs, mica, mice, mich, mick, mico, mida, midi,
mids, mien, miff, migo, migs, mike, mild, mile, milk, mill, mils, milt, mime,
mina, mind, mine, ming, mini, mink, mins, mint, minx, miny, mira, mire, mirk,
mirv, miry, misc, mise, miso, miss, mist, misy, mite, mitt, mitu, mity, mixt,
mktg, moan, moas, moat, mobs, mock, moco, mode, modi, modo, mods, mody, moff,
moha, moho, mohr, moil, moke, moky, mola, mold, mole, moll, molt, moly, mome,
moms, mona, mone, monk, mono, mons, mont, mony, mood, moon, moor, moos, moot,
mope, mops, mopy, mora, more, morn, moro, mort, mosk, moss, most, mote, moth,
moto, mots, moue, moun, move, mowe, mown, mows, moxa, moya, msec, muce, much,
muck, muds, muff, mugs, mule, mull, mumm, mump, mums, mund, mung, muon, mure,
murk, murr, musa, muse, mush, musk, muss, must, mute, mutt, muxy, myna, myth,
myxa,

 

4 letter words starting with "N"

nabk, nabs, nags, naid, naif, naik, nail, nais, nake, nale,
nall, name, namo, naos, nape, naps, napu, narc, nard, nare, nark, nart, nary,
nasa, nash, nath, natl, nato, naut, nave, navy, nawl, nays, nayt, naze, nazi,
neaf, neal, neap, near, neat, nebs, neck, need, neer, neif, nems, neon, nepa,
nerd, nere, nero, nese, nesh, ness, nest, nets, neve, nevi, news, newt, next,
nias, nibs, nice, nick, nide, nief, nigh, nile, nill, nils, nilt, nims, nine,
nips, nipt, nisi, nits, nixy, noah, nobs, nock, node, nods, noel, noes, nogs,
noie, noil, noir, nole, noll, nolo, nolt, noma, nome, noms, none, nook, noon,
noot, nope, norm, norn, nose, nosh, nost, nosy, nota, note, nots, nott, noun,
nous, nova, novo, nowd, nows, nowt, nubs, nude, nuke, null, numb, nuns, nurl,
nuts, nyas,

 

4 letter words starting with "O"

oafs, oaks, oaky, oars, oary, oast, oath, oats, obbe, obey,
obis, obit, oboe, obol, ocra, odal, odds, odes, odic, odin, odor, odyl, ofay,
offs, ogam, ogee, ogle, ogre, ohed, ohio, ohms, oils, oily, oink, oint, okay,
oker, okie, okra, olay, olds, olea, oleo, oles, olid, olio, olla, olpe, omen,
omer, omit, once, onde, ones, only, onto, onus, onyx, oohs, oops, ooze, oozy,
opah, opal, opec, open, opes, opie, opts, opus, opye, oral, orbs, orby, orca,
orch, orcs, ordo, ores, orfe, orgy, orig, orle, orlo, orth, orts, oryx, osar,
oslo, ossa, osse, otic, otis, otto, ouch, ours, ouse, oust, outs, ouze, ouzo,
oval, oven, over, ovid, ovum, owch, owed, owel, owen, owes, owls, owns, owre,
owse, oxen, oxes, oxid, oyer, oyes, oyez,

 

4 letter words starting with "P"

paas, paca, pace, pack, paco, pacs, pact, pacu, pads, page,
pahi, paid, pail, pain, pair, pais, pale, pali, pall, palm, palo, palp, pals,
paly, pane, pang, pans, pant, papa, pape, paps, para, pard, pare, park, parr,
pars, part, pash, pask, paso, pass, past, pate, path, pats, paul, paum, pave,
pavo, pawk, pawl, pawn, paws, payn, pays, peag, peak, peal, pean, pear, peas,
peat, peba, peck, peds, peed, peek, peel, peen, peep, peer, pees, pegm, pegs,
pein, peke, pela, pelf, pell, pelt, pend, penk, pens, pent, peon, pepo, peps,
pere, peri, perk, perm, pern, pers, pert, peru, pery, pese, peso, pest, pets,
pews, phew, phiz, phys, phyz, pial, pian, pica, pice, pici, pick, pics, pied,
pier, pies, piet, pigg, pigs, pika, pike, pile, pill, pily, pima, pimp, pina,
pine, ping, pink, pins, pint, piny, pion, piot, pipa, pipe, pips, pipy, pirl,
pirn, pisa, pise, pish, piss, pist, pita, pith, pits, pity, pius, pixy, pkwy,
plan, plat, play, plea, pled, pley, plim, ploc, plod, plop, plot, plow, ploy,
plug, plum, plus, pnyx, poak, pock, poco, pods, poem, poet, pogy, poke, poky,
pole, polk, poll, polo, pols, polt, poly, pome, pomp, pond, pone, pong, pons,
pony, pood, pooh, pool, poon, poop, poor, pope, pops, pore, pork, porn, port,
pory, pose, posh, poss, post, posy, pots, pott, pouf, poup, pour, pout, powp,
pows, poze, prad, pram, prat, pray, prep, pres, prey, prie, prig, prim, pris,
prix, proa, proc, prod, prof, prog, prom, pron, prop, pros, prow, prox, psst,
pubs, puce, puck, puds, pudu, pued, puer, puet, puff, pugh, pugs, puit, puke,
pule, pull, pulp, pult, pulu, puma, pume, pump, pumy, puna, pung, punk, puns,
punt, puny, puoy, pupa, pupe, pups, pure, puri, purl, purr, push, puss, puts,
putt, pyet, pyin, pyla, pyne, pyot, pyre, pyro,

 

4 letter words starting with "R"

raca, race, rach, rack, racy, rade, rads, raff, raft, raga,
rage, rags, raia, raid, rail, rain, raip, rais, raja, rake, raki, rale, rami,
ramp, rams, rana, rand, rang, rani, rank, rant, rape, raps, rapt, rara, rare,
rase, rash, rasp, rata, rate, rath, rats, rave, raws, rays, raze, razz, rcpt,
read, reak, real, ream, reap, rear, rebs, recd, reck, recs, rede, redo, reds,
reed, reef, reek, reel, reem, refs, reft, reif, reim, rein, reis, reit, rely,
reme, rems, rend, reng, reno, rent, reps, rese, resp, rest, retd, rete, reve,
revs, rewe, reyn, rhea, rhob, rhus, rial, ribs, rice, rich, rick, ride, rids,
rief, riel, rife, riff, rift, rigs, rile, rill, rily, rima, rime, rims, rimy,
rind, rine, ring, rink, riot, ripe, rips, rise, rish, risk, rist, rite, ritz,
rive, road, roam, roan, roar, robe, robs, rock, rocs, rode, rods, rody, roed,
roes, roil, roin, roke, roky, role, roll, rome, romp, roms, rong, ront, rood,
roof, rook, room, roon, roop, root, rope, ropy, rory, rosa, rose, ross, rost,
rosy, rota, rote, roto, rots, roty, roue, rouk, roun, roup, rout, roux, rove,
rown, rows, rube, rubs, ruby, ruck, rudd, rude, rued, ruer, rues, ruff, ruft,
ruga, rugs, ruin, rukh, rule, ruly, rump, rums, rune, rung, runs, runt, ruse,
rush, rusk, russ, rust, ruth, ruts, ryal, ryas, ryes, rynd, ryot, rysh, ryth,

 

4 letter words starting with "S"

saan, sack, sacs, sadh, sadr, safe, saga, sage, sago, sags,
sagy, saic, said, sail, saim, sain, sake, saki, sale, salm, salp, salt, same,
samp, sand, sane, sang, sank, sans, saps, sard, sari, sark, sarn, sart, sash,
sass, sate, sauf, sauh, saul, saur, saut, save, sawn, saws, says, scab, scad,
scag, scam, scan, scar, scat, scil, scop, scot, scow, scry, scud, scug, scum,
scup, scur, scut, scye, sdan, seah, seak, seal, seam, sean, sear, seas, seat,
seck, secs, sect, seed, seek, seel, seem, seen, seep, seer, sees, seet, sego,
seid, seke, seld, self, sell, sely, seme, semi, send, sens, sent, sept, sera, serb,
sere, serf, serr, sess, seta, sets, sett, sewe, sewn, sews, sext, sexy, seye,
seyh, shab, shad, shag, shah, sham, shat, shaw, shay, shed, shes, shet, shew,
shie, shim, shin, ship, shit, shiv, shmo, shod, shoe, shog, shoo, shop, shot,
show, shug, shul, shun, shut, siam, sibs, sice, sich, sick, sics, sida, side,
sift, sigh, sign, sike, sikh, sile, silk, sill, silo, silt, sima, simp, sine,
sing, sinh, sink, sins, sipe, sips, sipy, sire, sirs, sirt, sise, siss, sist,
site, sith, sits, situ, sitz, siva, size, sizy, skag, skar, skat, skee, skeg,
sken, skep, skew, skid, skim, skin, skip, skis, skit, skua, skue, skun, skys,
slab, slag, slam, slap, slat, slav, slaw, slay, sled, slee, slep, slew, sley,
slid, slik, slim, slip, slit, slob, sloe, slog, sloo, slop, slot, slow, slub,
slue, slug, slum, slur, slut, smee, smew, smit, smog, smug, smut, snag, snap,
snar, snaw, sneb, sned, snet, snew, snib, snig, snip, snit, snob, snod, snot,
snow, snub, snug, soak, soal, soam, soap, soar, sobs, sock, soda, sods, sofa,
sofi, soft, soho, soil, soja, soke, soko, sola, sold, sole, soli, solo, soly,
soma, some, sond, song, sons, soon, soot, sope, soph, sops, sora, sorb, sord,
sore, sori, sorn, sors, sort, sory, soss, sote, sots, soul, soun, soup, sour,
sous, sout, sowl, sown, sows, soya, soys, spad, spae, span, spar, spas, spat,
spaw, spay, spec, sped, sper, spet, spew, spic, spin, spit, spot, spry, spud,
spue, spun, spur, sput, stab, stag, stal, star, stat, staw, stay, sted, stee,
steg, stem, step, stet, stew, stey, stir, stoa, stop, stor, stot, stow, stre,
stub, stud, stum, stun, stut, stye, styx, subs, such, suck, sudd, suds, sued,
suer, sues, suet, suey, suez, sufi, suit, suji, sula, sulk, sull, sulu, sumo,
sump, sums, sung, sunk, sunn, suns, supe, sups, supt, sura, surd, sure, surf,
susu, swab, swad, swag, swal, swam, swan, swap, swat, sway, swig, swim, swob,
swom, swop, swum, syce, syke, syle, sync, syne, syrt, syth,

 

4 letter words starting with "T"

taas, tabs, tabu, tace, tach, tack, taco, tact, tads, tael,
taen, tags, taha, tahr, tail, tain, tait, take, talc, tale, tali, talk, tall,
tame, tamp, tams, tana, tang, tank, tans, tant, taos, tapa, tape, taps, tare,
tarn, taro, tarp, tars, tart, task, tass, tate, tath, tats, tatt, tatu, taur,
taut, taws, taxi, tbsp, tead, teak, teal, team, tear, teas, teat, tech, teds,
teed, teek, teel, teem, teen, tees, teil, tell, temp, tend, tene, tens, tent,
term, tern, terr, test, tete, teuk, text, thai, thak, than, thar, that, thaw,
thea, thee, them, then, thew, they, thin, this, thor, thou, thro, thru, thud,
thug, thus, tiar, tice, tick, tics, tide, tidy, tied, tier, ties, tiff, tift,
tigh, tike, tile, till, tilt, time, tind, tine, ting, tink, tins, tint, tiny,
tipi, tips, tire, tirl, tiro, tith, titi, tits, tivy, tiza, tnpk, toad, toat,
toby, toco, tody, toed, toes, toff, toft, tofu, toga, togo, togs, toil, toke,
tola, told, tole, toll, tolt, tolu, tomb, tome, toms, tone, tong, tons, tony,
took, tool, toom, toon, toot, tope, toph, topi, tops, tora, torc, tore, tori,
torn, toro, tors, tort, tory, tose, tosh, toss, tost, tota, tote, toto, tots,
toty, tour, tout, town, tows, towy, toys, toze, tozy, trad, tram, trap, tray,
tree, tref, trek, tren, tret, trew, trey, trig, trim, trio, trip, trod, tron,
trop, trot, trow, troy, trub, true, trug, tsar, tuba, tube, tubs, tuch, tuck,
tuet, tufa, tuff, tuft, tugs, tule, tull, tump, tuna, tune, tunk, tuns, tupi,
tups, turd, turf, turk, turm, turn, tush, tusk, tuts, tutu, tuum, tuza, twas,
twat, tway, twey, twig, twin, twit, twos, tydy, tyer, tyke, tymp, tynd, tyne,
tyny, type, typo, tyre, tyro, tzar,

 

4 letter words starting with "U"

udal, ufos, ughs, ugli, ugly, ukes, ulan, ulna, ulva, umbe,
umbo, umps, unau, unbe, unce, unci, unco, unde, undo, undy, unio, unit, univ,
unix, unke, unto, unty, unum, upas, upon, ural, urao, urbs, urds, urdu, urea,
urge, uric, urim, urns, urox, urry, ursa, urus, urva, used, usee, user, uses,
ussr, utah, utas, utes, utia, utis, utro, uvea, uvic,

 

4 letter words starting with "V"

vade, vail, vain, vair, vale, vamp, vane, vang, vans, vant,
vara, vare, vari, vark, vary, vasa, vase, vast, vats, vaut, veal, veda, veep,
veer, vees, vega, vehm, veil, vein, vela, veld, vele, vell, vena, vend, vent,
verb, verd, vers, vert, very, vese, vest, veto, vets, vial, vias, vice, vide,
vied, vier, vies, view, vild, vile, vill, vims, vina, vine, vino, vins, viny,
viol, vips, vire, visa, vise, vita, viva, vive, vivo, voce, void, vole, volt,
vote, vows, vrow, vugg, vugh, vugs, vyce,

 

4 letter words starting with "W"

waag, wack, wacs, wadd, wade, wadi, wads, wady, waeg, waft,
wage, wags, waid, waif, wail, wain, wair, wait, wake, wakf, wald, wale, walk,
wall, walm, walt, waly, wamp, wand, wane, wang, want, wany, wapp, ward, ware,
wark, warm, warn, warp, wars, wart, wary, wase, wash, wasp, wast, wats, watt,
waul, waur, wave, wavy, wawe, wawl, waxy, wayk, ways, weak, weal, wean, wear,
webs, weds, weed, week, weel, ween, weep, weet, weft, weir, weka, weld, wele,
welk, well, wels, welt, wend, wene, wens, went, wept, were, werk, wern, wert,
wesh, west, wets, wham, whan, whap, what, whee, when, whet, whew, whey, whig,
whim, whin, whip, whir, whit, whiz, whoa, whom, whop, whot, whur, whys, wich,
wick, wide, wier, wife, wigg, wigs, wike, wild, wile, wilk, will, wilt, wily,
wind, wine, wing, wink, wino, wins, winy, wipe, wire, wiry, wise, wish, wisp,
wist, wite, with, wits, wive, wkly, woad, wode, woes, woke, woks, wold, wolf,
woll, womb, wone, wong, wont, wood, woof, wook, wool, woon, woos, wops, word,
wore, work, worm, worn, wort, wost, wots, woul, wove, wowe, wowf, wows, wrap,
wraw, wray, wren, wrey, wrie, wrig, writ, wull, wust, wyes, wyke, wyla, wynd,
wynn, wype, wyte,

 

4 letter words starting with "X"

xeme, xiii, xmas, xvii, xxii, xxiv, xyst,

 

4 letter words starting with "Y"

yack, yaks, yale, yama, yamp, yams, yang, yank, yaps, yard,
yare, yark, yarn, yarr, yate, yaud, yaul, yaup, yawd, yawi, yawl, yawn, yawp,
yaws, yead, yeah, yean, year, yeas, yede, yeel, yegg, yelk, yell, yelp, yend,
yens, yerd, yerk, yern, yest, yeti, yeve, yews, yghe, yids, yift, yins, yipe,
yips, yite, yive, ymca, ymel, ynow, yode, yoga, yogi, yoit, yoke, yold, yolk,
yoll, yond, yoni, yore, york, yote, youl, your, yowe, yowl, yows, yren, yuan,
yuck, yuen, yuga, yuke, yuks, yule, yunx, yurt, yvel, ywar, ywca, ywis,

 

4 letter words starting with "Z"

zags, zaim, zain, zany, zaps, zarf, zati, zeal, zebu, zeds,
zees, zein, zend, zero, zest, zeta, zeus, zigs, zimb, zinc, zing, zink, zion,
zips, zobo, zoea, zoic, zona, zone, zoom, zoon, zoos, zope, zori, zubr, zulu,
zuni, zyme,

 

the question is a little confusing. the details help some what.
there are 2 words with one letter. there are about 10 to 20 two letter words. not really sure cause i counted in my head :-) theres more in you count contrations like "i'm."
you never said what your domain name is!