late Old English turnian "to rotate, revolve," in part also from Old French torner "to turn," both from Latin tornare "turn on a lathe," from tornus "lathe," from Greek tornos "lathe, tool for drawing circles," from PIE root *tere- "to rub, rub by turning, turn, twist" (see throw (v.)). Expression to turn (something) into (something else) probably retains the classical sense of "to shape on a lathe" (attested in English from c.1300). Related: Turned; turning.
To turn up "arrive" is recorded from 1755. Turn-off "something that dampens one's spirits" recorded by 1971 (said to have been in use since 1968); to turn (someone) on "excite, stimulate, arouse" is recorded from 1903. Someone should revive turn-sick "dizzy," which is attested from mid-15c. To turn (something) loose "set free" is recorded from 1590s. Turn down (v.) "reject" first recorded 1891, American English. Turn in "go to bed" is attested from 1690s, originally nautical. To turn the stomach "nauseate" is recorded from 1620s. To turn up one's nose as an expression of contempt is attested from 1779. Turning point is attested by 1836 in a figurative sense; literal sense from 1856.