Zest

google

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late 17th century (in sense zest (sense 2 of the noun)): from French zeste ‘orange or lemon peel’, from obsolete zec ‘membrane around walnut kernel’, ‘object of no importance’.

wiktionary

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Borrowed from French zeste. [1]

etymonline

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zest (n.)

1670s, from French zeste "piece of orange or lemon peel used as a flavoring," of unknown origin. Sense of "thing that adds flavor" is 1709; that of "keen enjoyment" first attested 1791.