(しり)

おしり
noun
buttocks, bottom
See also: (しり) (plain form)
1. buttocks, bottom
The fleshy part of the body that one sits on.
(しり)(いた)
My bottom hurts.
I wipe the baby's bottom.
My bottom went numb from sitting for a long time.

(しり) is the standard word for buttocks in everyday Japanese.

REGISTER:
The お prefix makes this a polite form. The plain form (しり) exists but sounds rougher. お(しり) is appropriate in most situations.

COMMON EXPRESSIONS:

ALTERNATIVES: