The Collaborative International Dictionary of English v.0.48:

Fanaticism \Fa*nat"i*cism\, n. [Cf. Fanatism.]
   Excessive enthusiasm, unreasoning zeal, or wild and
   extravagant notions, on any subject, especially religion,
   politics or ideology; religious frenzy.

   Syn: See Superstition.
        [1913 Webster]

WordNet (r) 3.0 (2006):

fanaticism
    n 1: excessive intolerance of opposing views [syn: fanaticism,
         fanatism, zealotry]