"woman to whom one is betrothed," 1844 (1837 as a French word in English), from French fiancée, fem. of fiancé, past participle of fiancer "to betroth," from fiance "a promise, trust," from fier "to trust," from Vulgar Latin *fidare "to trust," from Latin fidus "faithful" from the same root as fides "faith" (see faith). It has all but expelled native betrothed. The English verb fiance, now obsolete, was used c.1450-1600 for "to engage to be married."