1. Great excitement for or interest in a subject or cause.
2. A source or cause of great excitement or interest.
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.]
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Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.