Source : Webster's Revised Unabridged Dictionary (1913)

Enthusiasm \En*thu"si*asm\, n. [Gr. ?, fr. ? to be inspired or
   possessed by the god, fr. ?, ?, inspired: cf. enthousiasme.
   See {Entheal}, {Theism}.]
   1. Inspiration as if by a divine or superhuman power;
      ecstasy; hence, a conceit of divine possession and
      revelation, or of being directly subject to some divine
      impulse.

            Enthusiasm is founded neither on reason nor divine
            revelation, but rises from the conceits of a warmed
            or overweening imagination.           --Locke.

   2. A state of impassioned emotion; transport; elevation of
      fancy; exaltation of soul; as, the poetry of enthusiasm.

            Resolutions adopted in enthusiasm are often repented
            of when excitement has been succeeded by the wearing
            duties of hard everyday routine.      --Froude.

            Exhibiting the seeming contradiction of
            susceptibility to enthusiasm and calculating
            shrewdness.                           --Bancroft.

   3. Enkindled and kindling fervor of soul; strong excitement
      of feeling on behalf of a cause or a subject; ardent and
      imaginative zeal or interest; as, he engaged in his
      profession with enthusiasm.

            Nothing great was ever achieved without enthusiasm.
                                                  --Emerson.

   4. Lively manifestation of joy or zeal.

            Philip was greeted with a tumultuous enthusiasm.
                                                  --Prescott.

Source : WordNet®

enthusiasm
     n 1: a feeling of excitement
     2: overflowing with enthusiasm [syn: {exuberance}, {ebullience}]
     3: a lively interest; "enthusiasm for his program is growing"