adjective

1. so offensive to the senses as to cause disgust; stinking; loathsome a foul odor
2. extremely dirty or impure; disgustingly filthy
3. full of or blocked up with dirt or foreign objects a foul pipe
4. putrid; rotten: said of food
5. not decent; obscene; profane foul language
6. very wicked; abominable a foul murder
7. not clear; stormy; unfavorable foul weather, winds, etc.
8. tangled or snarled; caught a foul rope
9. not according to the rules of a game; unfair, by either accident or intention
10. treacherous; dishonest
11. Chiefly Brit., Now Dial. ugly
12. Informal unpleasant, disagreeable, etc.
13. ☆ Baseball of or having to do with the part of the field that lies outside the foul lines
14. Printing containing errors or marked with changes foul copy or proof

Etymology: ME < OE ful, akin to Ger faul, rotten, lazy < IE base *pū-, *pu-, to stink (< ? exclamation of disgust) > L putere, to rot, Gr pyon, pus

adverb

1. in a foul way
2. Baseball in or into the part of the field that lies outside the foul lines

noun

transitive verb

1. to make foul; dirty; soil; defile
2. to dishonor or disgrace
3. to impede or obstruct; specif.,
   1. to fill up; encrust; choke to foul a drain with grease
   2. to cover (the bottom of a ship) with barnacles, seaweed, etc.
   3. to entangle; catch a rope fouled in the shrouds
4. to make a foul against in a contest or game
5. ☆ Baseball to bat (the ball) so that it falls outside the foul lines

intransitive verb

1. to become dirty, filthy, or rotten
2. to be clogged or choked
3. to become tangled
4. to break the rules of a game
5. Baseball to bat the ball so that it falls outside the foul lines or is caught there to foul to the third baseman