polytheist (n.)

"belief in more gods than one," 1610s, from French polythéisme (16c.), formed from Greek polytheia "polytheism," polytheos "of or belonging to many gods," from polys "many" (from PIE root *pele- (1) "to fill") + theos "god" (from PIE root *dhes-, forming words for religious concepts).

The various modes of worship, which prevailed in the Roman world, were all considered by the people, as equally true; by the philosopher, as equally false; and by the magistrate, as equally useful. And thus toleration produced not only mutual indulgence, but even religious concord. [Gibbon]

word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.

Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.