Became mature and ready to eat, or became ready or suitable for something.
From Old English 'ripe' meaning mature or ready, plus '-ed' for past tense. The word originally referred to fruit becoming ready to harvest.
Bananas ripen differently depending on temperature—growers actually use the word 'mature' to mean picked-but-not-yet-yellow bananas, and 'ripened' for the yellow ones you buy, showing how commerce changes even basic food language.
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