mid-15c., opinen, "express an opinion or opinions; to think, suppose," also transitive, "be of the opinion that," from Old French oppiner, opiner (15c.) and directly from Latin opinari "have an opinion, be of opinion, suppose, conjecture, think, judge," which is of unknown origin. It is traditionally considered to be related to optare "to desire, choose" (see option), but de Vaan's sources find the evidence of this weak. Related: Opined; opining.