The Collaborative International Dictionary of English v.0.48:
Demonism \De"mon*ism\, n. [Cf. F. d['e]monisme.] The belief in demons or false gods. [1913 Webster] The established theology of the heathen world . . . rested upon the basis of demonism. --Farmer. [1913 Webster]WordNet (r) 3.0 (2006):
demonism n 1: a belief in and reverence for devils (especially Satan) [syn: diabolism, demonism, Satanism]