enthusiastic adj.

c. 1600, from French enthousiasme (16c.) and directly from Late Latin enthusiasmus, from Greek enthousiasmos "divine inspiration, enthusiasm (produced by certain kinds of music, etc.)," from enthousiazein "be inspired or possessed by a god, be rapt, be in ecstasy," from entheos "divinely inspired, possessed by a god," from en "in" (see en- (2)) + theos "god" (from PIE root *dhes-, forming words for religious concepts). It acquired a derogatory sense of "excessive religious emotion through the conceit of special revelation from God" (1650s) under the Puritans; generalized meaning "fervor, zeal" (the main modern sense) is first recorded 1716.

"characterized by sarcasm, bitterly cutting, scornfully severe," 1690s, from sarcasm, perhaps on the model of enthusiastic. Earlier adjectives were sarcastical (1640s); sarcasmous (1660s); sarcasmical (c. 1600). Related: Sarcastically.

1805, from un- (1) "not" + enthusiastic (adj.). Related: Unenthusiastically.