Merriam-Webster's Collegiate® Dictionary, 11th Edition
FOUL
I. adjective
Etymology: Middle English, from Old English fūl; akin to Old High German fūl rotten, Latin pus pus, putēre to stink, Greek pyon pus Date: before 12th century
1. offensive to the senses ; loathsome , filled or covered with offensive matter, full of dirt or mud,
3. morally or spiritually odious ; detestable , notably unpleasant or distressing ; wretched , horrid , obscene , abusive ,
5. being wet and stormy, obstructive to navigation , homely , ugly ,
7. treacherous , dishonorable , constituting an infringement of rules in a game or sport , containing marked-up corrections , encrusted, clogged, or choked with a foreign substance , being odorous and impure ; polluted , placed in a situation that impedes physical movement ; entangled, being outside the foul lines in baseball, see: dirty foully adverb foulness noun
II. noun Date: before 12th century something foul, an entanglement or collision especially in angling or sailing,
3. an infringement of the rules in a game or sport, free throw , foul ball ,
III. verb Date: before 12th century intransitive verb to become or be foul: as, decompose , rot , to become encrusted, clogged, or choked with a foreign substance, to become entangled or come into collision, to commit a violation of the rules in a sport or game, to hit a foul ball, transitive verb to make foul: as, to make dirty ; pollute , to tangle or come into collision with, to encrust with a foreign substance , obstruct , block , dishonor , discredit , to commit a foul against, to hit (a baseball) foul,
IV. adverb
Date: 13th century
in a foul manner ; so as to be foul