The most extreme or serious form of heresy; a belief that is considered the worst possible departure from religious orthodoxy.
From arch- (supreme, chief) + heresy (a belief contrary to religious doctrine). Heresy comes from Old French heresie, from Late Latin haeresis, from Greek hairesis (choice, sect).
The Medieval Church was obsessed with degrees of wrongness—archheresy was the nuclear option of theological crime, making some heresies worse than others, which is why records show careful hierarchies of sin and punishment.
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