posterior
noun
the fleshy part of the human body that you sit on
“he deserves a good kick in the butt”
“are you going to sit on your fanny and do nothing?”
a tooth situated at the back of the mouth
Synonymsback tooth
adjective
located at or near or behind a part or near the end of a structure
Oppositesanteriorcoming at a subsequent time or stage
“without ulterior argument”
“the mood posterior to”
Source: WordNet 3.1, Princeton University