Definition of zealot:

part of speech: noun

One who engages warmly and earnestly in any cause; one carried away by excess of zeal.

Usage examples:

• " And when I catch sight of his lordship," added the amiable zealot I'll astonish him. William Magnay in "A Poached Peerage".

• When the Prophet got down on his knees, Starr was silent; it looked as if this zealot intended to offer prayer- and the bank examiner did not care to earn the reputation of being a disturber of a religious gathering. Holman Day in "When Egypt Went Broke".

• Tall High- priest, with zealot fires Blazing in those eyeballs old, Swathes him, as his rank requires, Head to foot, in linen fold. Richard Doddridge Blackmore in "Fringilla: Some Tales In Verse".