rump (n.)

"hind-quarters, buttocks of an animal," mid-15c., from a Scandinavian source (compare Danish, Norwegian rumpe, Swedish rumpa), from or corresponding to Middle Dutch romp, German Rumpf "trunk, torso." Sense of "small remnant" derives from "tail" and is first recorded 1640s in reference to the English Rump Parliament (December 1648-April 1653). As an adjective from c. 1600.