Source : Webster's Revised Unabridged Dictionary (1913)

Mysticism \Mys"ti*cism\, n. [Cf. F. mysticisme.]
   1. Obscurity of doctrine.

   2. (Eccl. Hist.) The doctrine of the Mystics, who professed a
      pure, sublime, and wholly disinterested devotion, and
      maintained that they had direct intercourse with the
      divine Spirit, and aquired a knowledge of God and of
      spiritual things unattainable by the natural intellect,
      and such as can not be analyzed or explained.

   3. (Philos.) The doctrine that the ultimate elements or
      principles of knowledge or belief are gained by an act or
      process akin to feeling or faith.

Source : WordNet®

mysticism
     n 1: a religion based on mystical communion with an ultimate
          reality [syn: {religious mysticism}]
     2: obscure or irrational thought