Source : Webster's Revised Unabridged Dictionary (1913)

Enthusiast \En*thu"si*ast\, n. [Gr. ?: cf. F. enthousiaste.]
   One moved or actuated by enthusiasm; as:
   (a) One who imagines himself divinely inspired, or possessed
       of some special revelation; a religious madman; a
       fanatic.
   (b) One whose mind is wholly possessed and heated by what
       engages it; one who is influenced by a peculiar; fervor
       of mind; an ardent and imaginative person.

             Enthusiasts soon understand each other. --W.
                                                  Irving.

   Syn: Visionary; fanatic; devotee; zealot.

Source : WordNet®

enthusiast
     n 1: an ardent and enthusiastic supporter of some person or
          activity [syn: {partisan}, {partizan}]
     2: a person having a strong liking for something [syn: {fancier}]