尻
コウ, しり, がみ
buttocks, hips, butt, rear
JLPT0 G7 S5 F1692
As per
九
# (bump up against and bend/curve) +
尸
body/buttocks → the curvy *buttocks*, which curve upon coming into contact with other objects → *bottom*; *rear*; *end*.
[Full Kanji Etymology List]