The Greek word
As to the word itself, it is generally allowed to be of Greek extraction. But whence the Greek word enthousiasmos is derived, none has yet been able to show. Some have endeavored to derive it from en Theo, in God, because all enthusiasm has reference to him. But this is quite forced, there being small resemblance between the word derived and those they strive to derive it from. Others would derive it from en thusia, in sacrifice, because many of the enthusiasts of old were affected in the most violent manner during the time of sacrifice. Perhaps it is a fictitious word, invented from the noise which some of those made who were so affected.
1771 text
6. As to the word itself, it is generally allowed to be of Greek extraction. But whence the Greek word ἐνθουσιασμός, is derived, none has yet been able to shew. Some have endeavoured to derive it from ἐν Θεῷ, in God, because all Enthusiasm has reference to him. But this is quite forced; there being small resemblance between the word derived, and those they strive to derive it from. Others would derive it from ἐν θυσία, in sacrifice, because many of the Enthusiasts of old, were affected in the most violent manner, during the time of sacrifice. Perhaps it is a fictitious word, invented from the noise, which some of those made who were so affected.