Why is the ninth month called September?
"hind-quarters, buttocks of an animal," mid-15c., from a Scandinavian source (cf. 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.