past tense and past participle of lay (v.). Laid-up "injured, sick," originally was a nautical term (1769) describing a ship moored in harbor. Laid off "temporarily unemployed" is from 1916. Get laid "have sex" (with someone) attested from 1952, U.S. slang. Laid-back "relaxed" is first attested 1973, perhaps in reference to the posture of highway motorcyclists. Laid up "incapacitated" originally was of ships.