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[ih-kwey-ter] /ɪˈkweɪ tər/
the great circle on a sphere or heavenly body whose plane is perpendicular to the axis, equidistant everywhere from the two poles of the sphere or heavenly body.
the great circle of the earth that is equidistant from the North Pole and South Pole.
a circle separating a surface into two congruent parts.
Origin of equator
1350-1400; Middle English < Medieval Latin aequātor, Latin: equalizer (of day and night, as when the sun crosses the equator). See equate, -tor Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2017.
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Examples from the Web for equator
Contemporary Examples
Historical Examples
  • In theory it rises in the east and sets in the west; but in reality it only behaves so on or very near the equator.

    Woodcraft E. H. (Elmer Harry) Kreps
  • It was still dark, for the sun rises and sets at six o'clock on the equator.

    Four Young Explorers Oliver Optic
  • Ptolemy assumed that a degree at the equator was 500 stadia instead of 604 stadia in length.

  • Every point on the equator is, therefore, 90 from each pole.

    Lectures in Navigation Ernest Gallaudet Draper
  • Plants and animals spreading towards the equator would not be affected in the same way as others spreading from it.

  • They are nearly parallel to each other and to the planet's equator.

    The Story of the Heavens Robert Stawell Ball
British Dictionary definitions for equator


the great circle of the earth with a latitude of 0°, lying equidistant from the poles; dividing the N and S hemispheres
a circle dividing a sphere or other surface into two equal symmetrical parts
(astronomy) See celestial equator
Word Origin
C14: from Medieval Latin (circulus) aequātor (diei et noctis) (circle) that equalizes (the day and night), from Latin aequāre to make equal
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for equator

late 14c., from Medieval Latin aequator diei et noctis "equalizer of day and night" (when the sun is on the celestial equator, twice annually, day and night are of equal length), agent noun from Latin aequare "make equal" (see equate). Sense of "celestial equator" is earliest, extension to "terrestrial line midway between the poles" first recorded in English 1610s.

Online Etymology Dictionary, © 2010 Douglas Harper
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equator in Science

  1. An imaginary line forming a great circle around the Earth's surface, equidistant from the poles and in a plane perpendicular to the Earth's axis of rotation. It divides the Earth into the Northern and Southern hemispheres and is the basis from which latitude is measured.

  2. A similar circle on the surface of any celestial body.

  3. The celestial equator.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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equator in Culture

equator definition

An imaginary circle around the Earth, equidistant from the North Pole and South Pole.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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