from 1960s (rack was Navy slang for "bed" in 1940s). Meaning "instrument of torture" first recorded mid-15c. (verb meaning "to torture on the rack" is from early 15c.), perhaps from Ger. rackbank, originally an implement for stretching leather, etc. Fig. sense of "agony" is from 1590s. Mechanical meaning "toothed bar" is from 1797 (see pinion
). Meaning "set of antlers" is first attested 1945, Amer.Eng.; hence slang sense of "a woman's breasts" (especially if large), c.1980s. Off the rack in ref. to clothing is from 1962. Rack up "register accumulate, achieve" is first attested 1961, probably from method of keeping score in pool halls.
"gait of a horse," 1530 (implied in racking), perhaps from Fr. racquassure "racking of a horse in his pace," of unknown origin. Or perhaps a variant of rock
"clouds driven before the wind," c.1300, also "rush of wind, collision, crash," possibly from O.E. racu "cloud," reinforced by O.N. rek "wreckage, jetsam," or by influence of O.E. wræc "something driven." Originally a northern word, perhaps from an unrecorded Scand. cognate of O.E. racu. Often
confused with wrack
(q.v.), especially in phrase rack and ruin (1599). The distinction is that rack is "driven clouds;" wrack is "seaweed cast up on shore."