Synonyms for Foul:

adj.

abominable (adjective)
bad, reprehensible, contemptible, atrocious, obnoxious, repugnant, wretched, terrible, disgusting, odious.
base (adjective)
immoral, sordid, mean, ugly.
dirty (adjective)
mucky, grimy, slovenly, unclean.
evil (adjective)
baneful, destructive, offensive, wicked, terrible, evil, bad, damnable, monstrous, heinous, hideous, disgraceful, atrocious, abominable, sinful, reprehensible, repugnant, repulsive, repellent, calamitous, nefarious, sinister, loathsome, revolting, detrimental.
foul (adjective)
impure, repulsive, squalid, despicable, vicious, nasty, dishonorable, putrid, obscene, monstrous, horrid, offensive, malodorous, revolting, repellent, low, smutty, stinking, abhorrent, abominable, fetid, wicked, dirty, mucky, hateful, scatological, unfair, unjust, nefarious, loathsome, detestable, base, yucky, lewd, inequitable, unclean, filthy, icky, noisome, infamous, disgraceful, vile, coarse, raunchy, scurrilous, heinous, profane.
foul-smelling (adjective)
malodorous.
impure (adjective)
impure.
malevolent (adjective)
bitter, Black-hearted, churlish, malignant, venomous, nasty, hateful, vicious, baleful, evil, antagonistic, wicked, sinister, treacherous, hurtful, perfidious, ill-natured, spiteful, baneful, malicious, hostile, rancorous, vindictive, sullen, corrosive, malevolent, catty, virulent, mean.
mephitic (adjective)
mephitic.
obscene (adjective)
scatologic, gross.
offensive (adjective)
offensive, horrid, atrocious.
revolting (adjective)
repellent.
unclean (adjective)
dusty, squalid, fetid, mucky, shabby, murky, scruffy, impure, infectious, scatological, festering, obscene, putrid, sordid, disgusting, filthy, icky, grubby, slovenly, toxic, unhygenic, unsanitary, offensive, insalubrious, defiled, unclean, odious, dirty, septic, smutty, crummy, sloppy, dingy, grungy, muddy, grimy, untidy.
unjust (adjective)
discriminatory, one-sided, inequitable, unfair, venal, unsportsmanlike, unjustifiable, partial, partisan, unequal, unjust, uneven, prejudiced, biased.
wicked (adjective)
wicked.
yucky (adjective)
skanky, yucky.

adv.

beastly (adverb)
gross.

n.

perverted, unethical, deviant, amoral, immoral. fractious, sensitive, short-tempered, ribald, temperamental, moody, opprobrious, vulgar, lewd, irritable, bad-tempered, coarse, hot-tempered, irascible, touchy. like, corner, pain, ugly, chip, dribble, cross, delivery, horrid, ball, backhand, blast. defensive, front, onside, offside, backhanded, Reeky, mephitic, freestyle. disgusting (noun)
rank.
foul (noun)
repellent, fouled, inclement, distasteful, smutty, putrid, foul-smelling, unjust, skanky, repellant, foetid, out of bounds, offensive, loathsome, revolting, tangled, marked-up, congest, maculate, illegible, yucky, stinking, defile, unsportsmanlike, contaminate, afoul, filthy, wicked, clog, fetid, unsporting, unclean, noisome, cheating, choke, pollute, smelly, funky, unfair, back up, clog up, malodorous, loathly, dirty, nasty, vile, soiled, disgusting, repelling, befoul, disgustful, choke off.
foul play (noun)
choke, clog, soil, catch, tangle, dirty, jam, entangle, defile, pollute, stain, sully, contaminate, obstruct, muddy, snarl, block, taint.
unfair (noun)
dishonorable, dishonest.

v.

dirty (verb)
contaminate, putrefy, befoul, smear, sully, tarnish, muddy, dirty, taint, defile, soil, pollute, streak, besmirch, stain, smudge, smirch.
foul (verb)
soil, smear, jam, entangle, stain, clog, catch, tarnish, defile, pollute, smudge, besmirch, taint, block, sully, snarl, choke, befoul, contaminate.
hinder (verb)
burden, jam, constrain, baffle, catch, constipate, entrap, hamstring, clog, snarl, obstruct, counter, curb, bung, delay, brake, mire, bar, bottleneck, dam, handicap, impair, drag, encumber, entangle, impede, congest, check, restrict, stop, resist, block, fetter, inhibit, deter, oppose, thwart, frustrate, complicate, cripple, snag, plug, interrupt, restrain, choke, paralyze, hinder, stay, tangle, hamper, crimp, cramp, detain.

Other synonyms:

Two-cycle, scatologic, Reeky, bunt, horsepower, Despisable, raunchy, onside, turbine, ground out, Fescennine. barnyard, despicable, flooded, detestable, abhorrent, offside, contemptible, bawdy, liter, bat, obnoxious, ribald, rank, freestyle, backhanded, mephitic. antipathetic, wretched, infamous, scurrilous, engine, horrid. balk, mess up, profane, vulgar, lewd, muck up. coarse. low. rich, broad. fly. double, HIT, front. drive. ill-favored
ugly.
Other relevant words:
afoul, contemptible, base, vile, despicable, detestable, obnoxious, lewd, fouled, noisome, rank, infamous, horrid, abhorrent, low, gross, clog up, abominable, ribald, wretched, bawdy, sultry.

Usage examples for foul

  1. Who said to you, 'Those that will, be foul foul they will be'?" – Journeys Through Bookland V2 by Charles H. Sylvester
  2. By fair means or foul she must. – A Terrible Secret by May Agnes Fleming
  3. " I don't know," replied Ward; " their talk was so foul when we stopped the drove that we had to tie their mouths up." – The Boy Scouts Book of Stories by Various