en·thu·si·asm 
(ĕn-thzē-ăz′əm)
(ĕn-thzē-ăz′əm)n.
1. Great excitement for or interest in a subject or cause.
2. A source or cause of great excitement or interest.
3. Archaic
a. Ecstasy arising from supposed possession by a god.
b. Religious fanaticism.
[Late Latin enthūsiasmus, from Greek enthousiasmos, from enthousiazein, to be inspired by a god, from entheos, possessed : en-, in; see EN-2 + theos, god; see dhēs- in the Appendix of Indo-European roots.]