The present participle of 'adverse' as a verb; the act of opposing or turning against (archaic).
From the archaic verb 'adverse' (to oppose) + '-ing' suffix. This form is virtually unused in modern English, representing an older verbal usage where 'adverse' could actively describe the action of opposing rather than just the state of being opposed.
Most '-ing' words we use describe active actions, but 'adversing' is probably older than the '-ing' form on most other Latin-derived opposition words, showing how word forms can become outdated long before the root disappears.
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