WordNet sense 1 (the fleshy part of the human body that you sit on):

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

WordNet sense 2 (external female sex organs):

female genitalia, female genital organ, female genitals