Source : Webster's Revised Unabridged Dictionary (1913)

Lycanthropy \Ly*can"thro*py\, n. [Gr. ?: cf. F. lycanthropie.]
   1. The supposed act of turning one's self or another person
      into a wolf. --Lowell.

   2. (Med.) A kind of erratic melancholy, in which the patient
      imagines himself a wolf, and imitates the actions of that
      animal.

Source : WordNet®

lycanthropy
     n : (folklore) the magical ability of a person to assume the
         characteristics of a wolf