posterior
n. countable C1 Advanced US //ˌpɔˈstɪɹjɝ// UK //pɒstˈiəɹɪɐ// pos·te·ri·or
n. the part of your body that you sit on. It is a polite or slightly funny way to say 'bottom' or 'butt'.
n. the buttocks or hindquarters of a human or animal. Often used as a humorous euphemism in formal or medical contexts.
He slipped on the ice and landed right on his posterior.
The doctor noted a small bruise on the patient's posterior following the fall from the bicycle.
Borrowed from Latin posterior (“that comes or follows after; later, latter”).
Usage
Commonly used in the singular with a possessive pronoun.