Equation

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late Middle English: from Latin aequatio(n- ), from aequare ‘make equal’ (see equate).

wiktionary

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From Old French, from Latin aequātiō(“an equalizing”). Morphologically equate +‎ -ion

etymonline

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equation (n.)

late 14c., a term in astrology (from French équation, 14c.); general sense of "action of making equal" is from 1650s, from Latin aequationem (nominative aequatio) "an equal distribution, a sharing in common," noun of state from past participle stem of aequare (see equal (adj.)). Mathematical sense is from 1560s, on notion of equalizing the expressions; Chemistry sense is from 1807.