To make heretical; to introduce heresy into, or to pronounce someone a heretic.
From heretic (noun) + -ate (verb-forming suffix). A rare denominative verb formed by converting the noun 'heretic' into a verb form, allowing theologians to describe the act of becoming or being declared heretical.
To 'hereticate' someone was a legal and theological process—the church didn't just disagree with you, they formally declared you heretical through official procedures, which often had dire consequences.
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