also rat's-tail, from rat (n.) + tail (n.1). Used since 16c. of conditions, growths, or devices held to resemble a rat's long, hairless tail in any way, including "lank lock of hair" (1810); "end of a rope" (1867). Related: Rat-tailed. A rat-tail file (1744) is a fine, round file used for enlarging holes in metal.
"hind-quarters, back-end, or buttocks of an animal," the part to which the tail is attached, mid-15c., from a Scandinavian source (compare Danish, Norwegian rumpe, Swedish rumpa), from or corresponding to Middle Dutch romp, German Rumpf "trunk, torso."
Specifically of this part used as food by late 15c. The figurative sense of "small remnant, tail-end of anything" derives from the notion of "tail" and is recorded from 1640s in reference to the English Rump Parliament (December 1648-April 1653), so called from sitting after the expulsion of the majority of members of the Long Parliament in Pride's Purge. As an adjective from c. 1600. Also in 18c. and 19c. a verb, "to turn one's back to" as a snub.
"pertaining to or situated near a tail," 1660s, from Latin cauda "tail of an animal," which is of unknown origin, + -al (1).
bright star in the tail of the constellation Cygnus the Swan, by 1741, from Arabic Al Dhanab al Dajajah "the Hen's Tail."