Fanatic
a person affected by excessive zeal and enthusiasm, especially on religious subjects; one laboring under wild and extravagant notions of religion; an enthusiast; a visionary. In ancient Rome the term was applied to such as passed their time in temples, and who, pretending to be inspired by the divinity, would burst into wild and frantic gestures, utter pretended prophecies, cut themselves with knives, etc. Hence, the term has in modern times come to be applied to such as manifest a religious enthusiasm, uncontrolled by reason or experience. Fanaticism is sometimes applied in a wider sense to any excessive prepossession of the mind by ideas of any kind. It has prevailed under different forms in all ages of the world; and one of its most remarkable and dangerous features is the tendency that it has to spread over large masses of a people. The very earnestness of the fanatic serves to carry conviction to the minds of others. Among persons of this class were Madame Guyon, Joanna Southcott, and numerous others.