late Old English turnian "to rotate, revolve," in part also from Old French torner "to turn away or around; draw aside, cause to turn; change, transform; turn on a lathe" (Modern French tourner), both from Latin tornare "to polish, round off, fashion, turn on a lathe," from tornus "lathe," from Greek tornos "lathe, tool for drawing circles," from PIE root *tere- (1) "to rub, turn." Transitive sense in English is from c. 1300. Related: Turned; turning.
Use in expression to turn (something) into (something else) probably retains the classical sense of "to shape on a lathe." To turn up "arrive, make an appearance" is recorded from 1755. Turn about "by turns, alternately" is recorded from 1640s. 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 1640s in a figurative sense "point at which a decisive change takes place;" literal sense "point on which a thing turns; point at which motion in one direction ceases and that in another or contrary direction begins" is from 1660s.
c. 1300, "in circumference, in a circle, on every side," from phrase on round; see a- (1) + round (adj.). Rare before 1600. In sense of "here and there with no fixed direction" it is attested from 1776 in American English (British English prefers about). As a preposition, "on or along a circuit," late 14c.; "on all sides, encircling, about" 1660s; of time, by 1873. To have been around "gained worldly experience" is from 1927, U.S. colloquial; to get around to it is from 1864.