1610s, from French polythéisme (16c.), formed from Greek polytheia "polytheism," polytheos "of many gods," from polys "many" (see poly-) + theos "god" (see Thea).
The belief in more than one god. The ancient Greeks, for example, were polytheists; their gods included Apollo, Athena, Dionysus, and Zeus. (Compare monotheism.)