The present participle or gerund form of an archaic or dialectal verb 'gree,' meaning to agree, concur, or reach harmony.
From Old English 'grēon' and Middle English 'gree' meaning agreement or concord, with '-ing' forming the continuous or gerundial form.
Before 'agree' dominated English, 'gree' captured the sense of harmony and mutual satisfaction—greing was the medieval way of describing two people reaching consensus with implicit goodwill.
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