Making or treating someone as an enemy; the present participle of the verb 'enemy' used as a transitive verb.
From 'enemy' as a verb plus the '-ing' progressive suffix. This is a rarely-used verbal form treating 'enemy' as an active verb rather than just a noun.
This word barely exists in modern English—you're far more likely to hear 'making an enemy' or 'turning into an enemy,' which shows how some verb forms just don't survive into modern usage.
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