How to say it: Pronounced "koo," with a very puckered "u."
What it means: Literally, "ass."
When it's used: A building block of French potty-talk, it has a thousand uses: A film de cul is a porn flick; a beau cul is a "nice ass," and so on.
Raunchy relatives: Cul has some very naughty cognates:
enculer—to bugger.
se faire enculer—to get buggered, screwed over.
trou de cul—literally, the asshole.