The Collaborative International Dictionary of English v.0.48:
Polytheism \Pol"y*the*ism\, n. [Poly- + Gr. ? cf. F. polyth['e]isme.] The doctrine of, or belief in, a plurality of gods. [1913 Webster] In the Old Testament, the gradual development of polytheism from the primitive monotheism may be learned. --Shaff-Herzog. [1913 Webster]WordNet (r) 3.0 (2006):
polytheism n 1: belief in multiple Gods [ant: monotheism]