1520s, from Latin ambiguus "having double meaning, shifting, changeable, doubtful," adjective derived from ambigere "to dispute about," literally "to wander," from ambi- "about" (see ambi-) + agere "drive, lead, act" (see act). Sir Thomas More (1528) seems to have first used it in English, but ambiguity dates back to c.1400. Related: Ambiguously; ambiguousness.