An archaic or dialectal spelling of coin, a piece of metal currency.
This is a Middle English or Early Modern English variant spelling of 'coin', which comes from Old French 'coingne' (corner, wedge, die for stamping).
Old spellings like 'coyn' show us that English spelling wasn't standardized until very recently—even something as common as 'coin' had multiple accepted spellings just a few centuries ago.
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