buttocks, nates, arse, butt, backside, bum, buns, can, fundament, hindquarters, hind end, keister, posterior, prat, rear, rear end, rump, stern, ...

the fleshy part of the human body that you sit on

• body part — any part of an organism such as an organ or extremity

• torso, trunk, body — the body excluding the head and neck and limbs