1620s, in rhetoric, "proposition involving two statements, the acceptance of one implying the rejection of the other," from noun use of Medieval Latin alternativus "do one thing and then another, do by turns," from Latin alternus "one after the other, alternate, in turns, reciprocal," from alter "the other" (see alter). Of courses of action, from 1814. Of objects, etc., "the other of two which may be chosen," by 1836.