Relating to or constituting apostasy; of or characteristic of those who have abandoned their religious or political faith.
From 'apostate' with the suffix '-ical' (more formal than '-ic'). This older English form appears in religious texts and historical documents discussing faith abandonment.
Medieval theologians wrote about 'apostatical heresies' to describe beliefs they saw as dangerous spiritual betrayals—the more dramatic the language, the more seriously they took the threat.
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