Addition

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late Middle English: from Latin additio(n- ), from the verb addere (see add).

wiktionary

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Sense of “what is added” dates from 14th century, from Middle English addicioun, addition, from Old French adition, from Latin additiōnem, accusative singular of additiō, from addō(“add, put”).

etymonline

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addition (n.)

late 14c., "action of adding numbers;" c. 1400, "that which is added," from Old French adition "increase, augmentation" (13c.), from Latin additionem (nominative additio) "an adding to, addition," noun of action from past-participle stem of addere "add to, join, attach" (see add). Phrase in addition to "also" is from 1680s.