A state of mind which drives one to extreme and unreasonable speech or conduct.
A fanatic is ordinarily unbalanced in mind with regard to the subject of his lanaticism.
A religious fanatic is apt to be the' most extreme because nothing so deeply affects the mind as religion.
It was doubtless fanaticism that impelled the Jewish leaders to such unreasonable action against Christ, causing them to override the laws of judicial procedure in their fell purpose of destroying Him.
The same fanaticism against Christ is seen today in Russia, recently in Mexico, and among certain sects in almost every country.
New Catholic Dictionary