enthusiasm: [17] Enthusiasm has had a chequered semantic history. Like giddiness, it meant originally ‘state of being inspired by a god’. It comes ultimately from Greek énthous or éntheos ‘possessed, inspired’, a compound formed from the prefix en- ‘in’ and theós ‘god’ (as in English theology). From this in turn was derived the verb enthousiázein ‘be inspired’ and the noun enthousiasmós, which passed into English via Latin or French, still with the sense ‘divine inspiration’ (‘Doth he think they knew it by enthusiasm or revelation from heaven?’ Richard Baxter, Infants’ church membership and baptism 1651).
In the stern climate of Puritanism, however, divine inspiration was not something to be encouraged, and as the 17th century progressed enthusiasm took on derogatory connotations of ‘excessive religious emotion’. The modern approbatory meaning, ‘eagerness’, had its beginnings at the start of the 18th century, and by the early 19th century had ousted the deprecatory sense from leading place. => theology
c. 1600, from Middle 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" (see theo-). 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.
