Sense of "act of good will" is recorded from c. 1300. Meaning "spell of work" is from late 14c.; that of "an individual's time for action, when these go around in succession" is recorded from late 14c. The automatic automobile turn-signal is from 1915. Turn-sick "dizzy," is attested from early 15c. Phrase done to a turn (1780) suggests meat roasted on a spit. The turn of the screw (1796) is the additional twist to tighten its hold, sometimes with reference to torture by thumbscrews.
late 14c. variant of earlier stomake (early 14c.), "internal pouch into which food is digested," from Old French stomaque, estomac "stomach," from Latin stomachus "throat, gullet; stomach," also "taste, inclination, liking; distaste, dislike;" also "pride, indignation," which were thought to have their origin in that organ (source also of Spanish estómago, Italian stomaco), from Greek stomachos "throat, gullet, esophagus," literally "mouth, opening," from stoma "mouth" (see stoma).
Applied anciently to the openings of various internal organs, especially that of the stomach, then by the later Greek physicians to the stomach itself. The native word is maw (Old English maga glosses stomachus).
Some 16c. anatomists tried to correct the sense back to "esophagus" and introduce ventricle for what we call the stomach. Meaning "belly, midriff, part of the body that contains the stomach" is from late 14c.
In Middle English also stomack, stomac, stommak, stomoke; the spelling of the ending of the word was conformed to Latin regularly from 16c., but the pronunciation remains as in Middle English. Related: stomachial (1580s); stomachical (c. 1600); stomachic (1650s). Pugilistic stomacher "punch in the stomach" is from 1814; from mid-15c. as "vest or other garment which covers the belly." The Latin figurative senses also were in Middle English (such as "relish, inclination, desire," mid-15c.) or early Modern English. Also sometimes regarded in Middle Ages as the seat of sexual desire.
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.