keister n : 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?" [syn: {buttocks}, {nates}, {arse}, {butt}, {backside}, {bum}, {buns}, {can}, {fundament}, {hindquarters}, {hind end}, {posterior}, {prat}, {rear}, {rear end}, {rump}, {stern}, {seat}, {tail}, {tail end}, {tooshie}, {tush}, {bottom}, {behind}, {derriere}, {fanny}, {ass}]