The fleshy part of the human body that you sit on. Synonyms: arse, ass, backside, behind, bottom, bum, buns, butt, can, derriere, fanny, fundament, hind end, hindquarters, keister, nates, posterior, prat, rear, rear end, rump, seat, stern, tail, tail end, tooshie, tush. "Are you going to sit on your fanny and do nothing?"