The belief in more than one god. The ancient Greeks, for example, were polytheists; their gods included Apollo, Athena, Dionysus, and Zeus. (Comparemonotheism.)
1613, from Fr. polythéisme (16c.), formed from Gk. polytheos "of many gods," from polys "many" (see poly-) + theos "god" (see Thea). Polytheist first attested 1619.