Synonyms:
fanatic, fanatical, overzealous, rabid
Meaning: marked by excessive enthusiasm for and intense devotion to a cause or idea; "rabid isolationist"
Usage examples
A few fanatical men, who had made it the vehicle of violent expressions, had kept it under the ban of popular prejudice.
What the Science Community was, no one knew exactly; but that there was something abnormal, fanatical, about it, no one doubted.
Though I am fully persuaded that he was some fanatical enthusiast, well meaning perhaps, but utterly ignorant of true piety; yet I could not forbear weeping at his words, spoken so unexpectedly at that particular period."
The sad thing about it is the fact that it is divided up into various chapels, each held by sects of so-called Christians, and a large-armed guard has to be kept in the church to keep these fanatical people from killing each other.