Latin 'aequator' (the equalizer) — the line where day and night are equal, twelve hours each at the equinoxes.
An imaginary line drawn around the earth equally distant from both poles, dividing the earth into Northern and Southern hemispheres.
From Medieval Latin 'aequātor' (in the phrase 'circulus aequātor diēī et noctis,' the circle equalizing day and night), agent noun from 'aequāre' (to make equal, to level, to balance), from 'aequus' (equal, level, flat, fair), from PIE *aik- or *h₂ei- (to give, to allot fairly — possibly related to notions of justice). Latin 'aequus' generated one of the largest clusters of English vocabulary: 'equal,' 'equality,' 'equity' (fairness), 'equinox' (equal night, when day equals night), 'equilateral' (equal-sided), 'equivalent,' 'adequate' (made equal to the need), 'equation' (setting two things equal), 'equilibrium' (equal balance), and 'equanimity' (even-tempered, balanced spirit). The equator is literally 'the equalizer' — the great circle where the sun's path
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