Enthusiasm (Greek: enthousiasmos) originally meant inspiration or possession by a divine afflatus or by the presence of a God. Johnson's Dictionary, the first comprehensive dictionary of the English language, divines enthusiasm as "a vain belief of private revelation; a vain confidence of divine favour or communication." In vernacular English today the word simply means intense enjoyment, interest or approval.
A distemper of youth, curable by small doses of repentance in connection with outward applications of experience. Byron, who recovered long enough to call it "entuzy-muzy," had a relapse, which carried him off -- to Missolonghi.