foul

Etymology 1

From Middle English foul, from Old English fūl (“foul, unclean, impure, vile, corrupt, rotten, guilty”), from Proto-West Germanic *fūl, from Proto-Germanic *fūlaz (“foul, rotten”), from Proto-Indo-European *puH- (“to rot”). Cognate with Dutch vuil (“foul”), German faul (“rotten, putrid”), Danish and Swedish ful (“foul”), and through Indo-European, with Albanian fëlliq (“to make dirty”), Latin puter (“rotten”). More at putrid. Ancient Greek φαῦλος (phaûlos, “bad”) is a false cognate inasmuch as it is not from the same etymon, instead being cognate to few.

adj

1. Covered with, or containing unclean matter; dirty.
   This cloth is too foul to use as a duster.
   His foul hands got dirt all over the kitchen.
   The air was so foul nobody could breathe.
   A ship's bottom is foul when overgrown with barnacles
   A well is foul with polluted water.
   It was, however, most interesting work, and the moulders themselves were a decent crowd, never tired of making jokes about themselves such as the hoary one that moulders did not live long, which however ran counter to the other one that no germs could live in a foundry—the atmosphere was too foul. 1944 November and December, A Former Pupil, “Some Memories of Crewe Works—II”, in Railway Magazine, page 342
   Since the mid-1980s, when Indonesia first began to clear its bountiful forests on an industrial scale in favour of lucrative palm-oil plantations, “haze” has become an almost annual occurrence in South-East Asia. The cheapest way to clear logged woodland is to burn it, producing an acrid cloud of foul white smoke that, carried by the wind, can cover hundreds, or even thousands, of square miles. 2013-06-29, “Unspontaneous combustion”, in The Economist, volume 407, number 8842, page 29
2. (of words or a way of speaking) Obscene, vulgar or abusive.
   The rascal spewed forth a series of foul words.
   His foul language causes many people to believe he is uneducated.
3. Detestable, unpleasant, loathsome.
   He has a foul set of friends.
4. Disgusting, repulsive; causing disgust.
   This foul food is making me retch.
   There was a foul smell coming from the toilet.
5. (obsolete) Ugly; homely; poor.
6. (of the weather) Unpleasant, stormy or rainy.
   Some foul weather is brewing.
7. Dishonest or not conforming to the established rules and customs of a game, conflict, test, etc.
   Foul play is not suspected.
8. (nautical) Entangled and therefore restricting free movement, not clear.
   We've got a foul anchor.
   A rope could get foul while it is being paid out.
9. (technical) (with "of") Positioned on, in, or near enough to (a specified area) so as to obstruct it.
   The bus had stopped just foul of the north track at the Erindale Station Road public railway crossing […] With the bus stationary, but still foul of the north track, the train struck one of its front mirrors. 2015, Transportation Safety Board of Canada, Railway Investigation Report R13T0192
10. (baseball) Outside of the base lines; in foul territory.
    Jones hit foul ball after foul ball.

Etymology 2

From Middle English foulen, fulen, from Old English fūlian (“to become foul; rot; decay”), from Proto-West Germanic *fūlēn, from Proto-Germanic *fūlāną (“to rot; decay”).

verb

1. (transitive) To make dirty.
   to foul the face or hands with mire
   She's fouled her diaper.
2. (transitive) To besmirch.
   He's fouled his reputation.
3. (transitive) To clog or obstruct.
   The hair has fouled the drain.
   As a result of the accident at Southend Airport when a Hermes aircraft overshot the runway and fouled the down Shenfield to Southend Victoria line between Rochford and Prittlewell, the Eastern Region is considering warning arrangements, which have already been provided on some lines running past aerodromes. 1961 November, “Talking of Trains: Aircraft on rail tracks”, in Trains Illustrated, page 650
4. (transitive, nautical) To entangle.
   The kelp has fouled the prop.
   The Indian's heart was sore for his boat; it looked as if nothing could save her. She was drifting more slowly now, her propeller fouled in kelp. 1941, Emily Carr, chapter 18, in Klee Wyck
5. (transitive, basketball) To make contact with an opposing player in order to gain advantage.
   Smith fouled him hard.
6. (intransitive, basketball) To commit a foul.
   Smith fouled within the first minute of the quarter.
7. (transitive, baseball) To hit outside of the baselines.
   Jones fouled the ball off the facing of the upper deck.
8. (intransitive, baseball) To hit a ball outside of the baselines.
   Jones fouled for strike one.
9. (intransitive) To become clogged.
   The drain fouled.
10. (intransitive) To become entangled.
    The prop fouled on the kelp.
11. To come into contact or collide with.
    The full capacity, however, requires a hopper of a size that takes the wagon body up to 11ft 11½in above rail level, which would foul many existing colliery screens. 1963 July, “News and Comment: The future of coal by rail”, in Modern Railways, page 5

noun

1. (sports) A breach of the rules of a game, especially one involving inappropriate contact with an opposing player in order to gain an advantage; for example, tripping someone up in soccer, or contact of any kind in basketball.
   A second Norwich goal in four minutes arrived after some dire Newcastle defending. Gosling gave the ball away with a sloppy back-pass, allowing Crofts to curl in a cross that the unmarked Morison powered in with a firm, 12-yard header. Gosling's plight worsened when he was soon shown a red card for a foul on Martin. December 10, 2011, Arindam Rej, “Norwich 4 - 2 Newcastle”, in BBC Sport
2. (bowling) A (usually accidental) contact between a bowler and the lane before the bowler has released the ball.
3. (baseball) A foul ball, a ball which has been hit outside of the base lines.
   Jones hit a foul up over the screen.