Surplus

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late Middle English: from Old French sourplus, from medieval Latin superplus, from super- ‘in addition’ + plus ‘more’.

wiktionary

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From Middle English surplus, from Middle French surplus. Compare French surplus.

etymonline

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surplus (n.)

late 14c., from Old French sorplus "remainder, extra" (12c., Modern French surplus), from Medieval Latin superplus "excess, surplus," from Latin super "over" (see super-) + plus "more" (see plus). As an adjective from late 14c.