"frame with bars," c.1305, possibly from M.Du.
rec "framework," related to
recken "stretch out," cognate with O.E.
reccan "to stretch out," from P.Gmc.
*rakjanan (cf. O.N.
rekja, O.Fris.
reza, O.H.G.
recchen, Ger.
recken, Goth.
uf-rakjan "to stretch out"). The verb meaning "to sleep" is teen-ager slang from 1960s (
rack was Navy slang for "bed" in 1940s). Meaning "instrument of torture" first recorded c.1460 (verb meaning "to torture on the rack" is from 1433), perhaps from Ger.
rackbank, originally an implement for stretching leather, etc. Fig. sense of "agony" is from 1591. 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.