An archaic or formal variant of antiatheistic, meaning opposed to atheism or supporting belief in God.
From 'anti-' (against) + 'atheistical,' an older English adjectival form of atheist using the '-ical' suffix common in Early Modern English. This variant appears in 17th-18th century theological writings.
You'd mainly find this fancy '-ical' version in old religious debates and philosophical texts—it's the verbose, formal-register cousin of 'antiatheistic'!
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