けつ

Etymology 1
From.

Noun

 * 1)  ass; arse; buttocks
 * 2)  last or hindermost part
 * 3)  gay sex, sex between two men
 * 1)  gay sex, sex between two men
 * 1)  gay sex, sex between two men

Usage notes

 * Almost never written as kanji, presumably to avoid ambiguity with.