Meaning of “foul” - Learner’s Dictionary

foul

adjective uk us /faʊl/
DIRTY

very dirty, or with an unpleasant smell:

the foul smell of rotting fish
BAD

very bad or unpleasant:

foul weather
She's in a foul mood.
foul language/words

very rude and offensive words

(Definition of “foul adjective” from the Cambridge Learner’s Dictionary © Cambridge University Press)