equator

[ih-kwey-ter]
noun
1.
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.
2.
the great circle of the earth that is equidistant from the North Pole and South Pole.
3.
a circle separating a surface into two congruent parts.

Origin:
1350–1400; Middle English < Medieval Latin aequātor, Latin: equalizer (of day and night, as when the sun crosses the equator). See equate, -tor

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World English Dictionary
equator (ɪˈkweɪtə)
 
n
1.  the great circle of the earth with a latitude of 0°, lying equidistant from the poles; dividing the N and S hemispheres
2.  a circle dividing a sphere or other surface into two equal symmetrical parts
3.  See magnetic equator
4.  astronomy See celestial equator
 
[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 10th Edition
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Etymonline
Word Origin & History

equator
late 14c., from M.L. 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), from L. aequare "make equal, 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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American Heritage
Science Dictionary
equator   (ĭ-kwā'tər)  Pronunciation Key 


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  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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American Heritage
Cultural Dictionary

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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Example sentences
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.
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