Present participle of aroint; the act of driving away or banishing.
From 'aroint' with the present participle suffix '-ing,' which comes from Old English '-ung' and has been the standard way to form gerunds and present participles since Old English times.
The '-ing' suffix is one of the most ancient and productive formations in English—it works on almost every verb, new or old, which is why we can instantly understand 'arointing' even though we've never seen 'aroint' before.
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