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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. 2015.
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Examples from the web for equator
  • It tends to be thickest over equatorial regions and thinnest over the poles.
  • Such storms arise to adjust imbalances that occur as the atmosphere transfers latent heat from the equator to the poles.
  • In addition, as you move away from the equator, smaller changes in altitude make a bigger difference in habitat conditions.
  • The orbit of the satellite is inclined 33 degrees to the equator.
  • It was midafternoon, and being near the equator in late January, it was above 90 degrees.
  • The sun returns to the equator on March 21, the spring equinox.
  • At the equator, the Sun is overhead at noon.
  • Declination is often used to orient to the stars, in relationship to the celestial equator.
  • But sunlight is strongest in the day, at the equator and in summer.
  • Its glossy sheen was fading, its arctic circle receding; the blue line of its equator quaked and bulged.
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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