The Collaborative International Dictionary of English v.0.48:

Polytheist \Pol"y*the*ist\, n. [Cf. F. polyth['e]iste.]
   One who believes in, or maintains the doctrine of, a
   plurality of gods.
   [1913 Webster] Polytheistic

WordNet (r) 3.0 (2006):

polytheist
    n 1: one who believes in a plurality of gods

Moby Thesaurus II by Grady Ward, 1.0:

21 Moby Thesaurus words for "polytheist":
   allotheist, anthropolater, anthropotheist, autotheist, cosmotheist,
   deist, ditheist, dualist, henotheist, hylotheist, monotheist,
   multitheist, myriotheist, pantheist, physitheist, psychotheist,
   tetratheist, theist, theriotheist, tritheist, zootheist