Variation

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late Middle English (denoting variance or conflict): from Old French, or from Latin variatio(n- ), from the verb variare (see vary).

wiktionary

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From Middle French variation, from Old French variacion, from Latin variātiō.

etymonline

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variation (n.)

late 14c., "difference, divergence," from Old French variacion "variety, diversity" and directly from Latin variationem (nominative variatio) "a difference, variation, change," from past participle stem of variare "to change" (see vary). The musical sense is attested from 1801. Related: Variational.