What does "zealot" mean?

Zealot: One who is zealous; one who engages warmly in any cause, and pursues his object with earnestness and ardor; especially, one who is overzealous, or carried away by his zeal; one absorbed in devotion to anything; an enthusiast; a fanatical partisan. Zealots for the one [tradition] were in hostile array against zealots for the other. Sir J. Stephen. In Ayrshire, Clydesdale, Nithisdale, Annandale, every parish was visited by these turbulent zealots. Macaulay.