The Collaborative International Dictionary of English v.0.48:

Demonolatry \De`mon*ol"a*try\, n. [Gr. dai`mwn demon + latrei`a
   worship, ? to serve, worship: cf. F. d['e]monol[^a]trie.]
   The worship of demons.
   [1913 Webster]

WordNet (r) 3.0 (2006):

demonolatry
    n 1: the acts or rites of worshiping devils [syn: diabolatry,
         demonolatry, devil-worship]