rear end
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?
Synonym: arse, keister, nates, posterior, prat, rear, rump, seat, stern, tail, tail end, tooshie, hindquarters, hind end, fundament, ass, backside, behind, bottom, bum, buns, butt, buttocks, can, derriere, fanny, tush