Other forms: befouled
To befoul is to make something filthy. Befoul the water, befouled with mud, befoul the air.
It is formal and carries disgust, which is why it appears in complaints and in older writing about pollution. Note the be- prefix, which turns an adjective into a verb meaning to make so — befoul, becalm, belittle.
1verbbefoulTo make something filthy.
“Waste from the factory befouled the river and killed the fish.”
befoul is a dirtying.
Also accepted in games: foul
Be- plus foul, from Old English ful, rotten or dirty. The be- prefix turns the adjective into a verb meaning to make so.
Proto-Indo-European
*puH- — foul, rotten
Proto-Germanic
*fūlaz — foul, rotten
Proto-West Germanic
*fūl
Old English
fūl — foul, dirty, unclean, impure, vile, corrupt, rotten, stinking, guilty
Middle English
ffoul
English
foul
English, today
befoul
From be + foul. foul Middle English ffoul, foul, foull, fowel, fowle, fuyle, voul, vul, from Old English fūl (“foul, dirty, unclean, impure, vile, corrupt, rotten, stinking, guilty”), from Proto-West Germanic fūl, from Proto-Germanic fūlaz (“foul, rotten”), from Proto-Indo-European puH- (“foul, rotten”). 2 Cognate with gmw-cfr fuul (“putrid, rotten; lazy, workshy”), cim baul, vaul (“putrid, rotten”), Dutch vuil (“dirty, foul; lewd, obscene; dishonorable; illegal”), German faul (“foul, putrid, rotten; lazy”), Yiddish פֿױל (“putrid; lazy”), Danish ful (“nasty, ugly”), Icelandic fúll (“foul, rotten, sullen”), Norwegian Bokmål and Norwegian Nynorsk ful (“clever, sly”), and Swedish ful (“ugly; bad, dirty”), Gothic 𐍆𐌿𐌻𐍃 (“fetid, foul, putrid”), and through Indo-European, with Latin puter (“decaying, rotten; friable, crumbling”), Greek πύο, πύον (“pus”), Albanian fëlliq (“to make dirty, sully”), Latvian pūt (“to rot”), Lithuanian pūti (“to rot”), Armenian փուտ (“rottenness”), Persian پوده (“rubbed, worn; foul, rotten; empty, hollow”), Sanskrit पूयति (“to become foul; to stink”). More at putrid.
Etymology from Wiktionary, CC BY-SA