/ ɪˈkweɪtə(r); NAmE / (usually the equator ) noun
[ sing. ] an imaginary line around the earth at an equal distance from the North and South Poles
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WORD ORIGIN
late Middle English : from medieval Latin aequator , in the phrase circulus aequator diei et noctis circle equalizing day and night, from Latin aequare make equal, from aequus even, level, equal.