Emily Dickinson Lexicon

EN-THU'SI-ASM, n. [enthu'ziazm; Gr. ενθουσιασμος, from ενθουσιαζω, to infuse a divine spirit, from ενθους, ενθεος, inspired, divine; εν and θεος, God.]

1. A belief or conceit of private revelation; the vain confidence or opinion of a person, that he has special divine communications from the Supreme Being, or familiar intercourse with him. Enthusiasm is founded neither on reason nor divine revelation, but rises from the conceits of a warmed or overweening imagination. Locke.
2. Heat of imagination; violent passion or excitement of the mind, in pursuit of some object, inspiring extravagant hope and confidence of success. Hence the same heat of imagination, chastised by reason or experience, becomes a noble passion, an elevated fancy, a warm imagination, an ardent zeal, that forms sublime ideas, and prompts to the ardent pursuit of laudable objects. Such is the enthusiasm of the poet, the orator, the painter and the sculptor. Such is the enthusiasm of the patriot, the hero and the Christian. Faction and enthusiasm are the instruments by which popular governments are destroyed. Ames.