A person who regards his own faith and views in matters of religion as unquestionably right, and any belief or opinion opposed to or differing from them as unreasonable or wicked. In an extended sense, a person who is intolerant of opinions which conflict with his own, as in politics or morals; one obstinately and blindly devoted to his own church, party, belief, or opinion.
An obstinate and intolerant holder of particular religious opinions, who refuses to listen to reason and is ready to force others to agree with him. The term arrived in English via French, having originated centuries earlier among Germanic/Frankish tribes of Gaul. Bei Gott (By God) mocked the exclamation frequently used by the crusading Christian missionaries who were bludgeoning the tribes into conversion.