backside

backside (http://definr.com/backside)

     n 1: the side of an object that is opposite its front; "his room
          was toward the rear of the hotel" [syn: rear, {back
          end}] [ant: front]
     2: the fleshy part of the human body that you sit on [syn: buttocks,
         nates, arse, butt, bum, buns, can, fundament,
         hindquarters, hind end, keister, posterior, prat,
         rear, rear end, rump, stern, seat, tail, {tail
        end}, tooshie, tush, bottom, behind, derriere, fanny,
         ass]