"hindmost part of an animal," Old English tægl, tægel, from Proto-Germanic *tagla- (cf. Old High German zagal, German Zagel "tail," dialectal German Zagel "penis," Old Norse tagl "horse's tail"), from PIE *doklos, from root *dek- "something long and thin" (referring to such things as fringe, lock of hair, horsetail; cf. Old Irish dual "lock of hair," Sanskrit dasah "fringe, wick"). The primary sense, at least in Germanic, seems to have been "hairy tail," or just "tuft of hair," but already in Old English the word was applied to the hairless "tails" of worms, bees, etc. Another Old English word for "tail" was steort (see stark).
Meaning "reverse side of a coin" is from 1680s; that of "backside of a person, buttocks" is recorded from c.1300; slang sense of "pudenda" is from mid-14c.; that of "woman as sex object" is from 1933, earlier "prostitute" (1846). The tail-race (1776) is the part of a mill race below the wheel. To turn tail "take flight" (1580s) originally was a term in falconry. The image of the tail wagging the dog is attested from 1907.
"limitation of ownership," a legal term, early 14c. in Anglo-French; late 13c. in Anglo-Latin, in most cases a shortened form of entail.
"follow secretly," U.S. colloquial, 1907, is from earlier sense of "follow or drive cattle," from tail (n.1). Related: Tailed; tailing. Tail off "diminish" is attested from 1854.
The posterior part of an animal, especially when elongated and extending beyond the trunk or main part of the body.
: tailing a jewelry salesman (1907+)
one's ass off, drag-tail, drag one's tail, get one's tail in a gate, have a broom up one's ass, have a tiger by the tail, have someone or something by the tail, piece of ass, ringtail, shavetail, work one's ass off
[in the second noun sense, tail, ''sex organ,'' is found by 1362]