Apiece

google

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late Middle English: from a1 + piece.

wiktionary

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From Middle English a pece, equivalent to a +‎ piece. [1] [2]

etymonline

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apiece (adv.)

"for each" (thing, person, etc.), 1550s, a contraction of a pece (mid-15c.), originally of coins, objects for sale, etc. (see a (2) + piece (n.1)).