Definition from Wiktionary, the free dictionary
zealot (plural zealots)
- One who is zealous, one who is full of zeal for his own specific beliefs or objectives, usually in the negative sense of being too passionate; a fanatic
- (historical) A member of a radical, warlike, ardently patriotic group of Jews in Judea, particularly prominent in the first century, who advocated the violent overthrow of Roman rule and vigorously resisted the efforts of the Romans and their supporters to convert the Jews.
- (historical) A member of an anti-aristocratic political group in Thessalonica from 1342 until 1350.
- 1733: For modes of faith, let graceless zealots fight; / His can't be wrong whose life is in the right — Alexander Pope, Essay on Man, Epistle III
- 1892: Yet Brahmans rule Benares still, / Buddh-Gaya's ruins pit the hill, / And beef-fed zealots threaten ill / To Buddha and Kamakura. — Rudyard Kipling, Buddha at Kamakura
Related terms 
member of the Zealot movement in Judea