"put or set down," 17c. adjectival use of past tense and past participle of lay (v.). Laid-up "injured, sick, incapacitated," originally was a nautical term (1769) describing a ship moored in harbor. Laid off "temporarily unemployed" is from 1916 (see layoff). Slang get laid "have sex" (with someone) attested from 1952, American English. Laid-back (adj.) "relaxed" is first attested 1973, perhaps in reference to the posture of highway motorcyclists.