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[ee-kwuh-noks, ek-wuh-] /ˈi kwəˌnɒks, ˈɛk wə-/
the time when the sun crosses the plane of the earth's equator, making night and day of approximately equal length all over the earth and occurring about March 21 (vernal equinox or spring equinox) and September 22 (autumnal equinox)
either of the equinoctial points.
1350-1400; Middle English < Medieval Latin equinoxium, for Latin aequinoctium the time of equal days and nights (aequi- equi- + noct- (stem of nox) night + -ium -ium) Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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Examples from the web for equinox
  • Magnetic activity is at a minimum in winter, and increases through equinox to a maximum in summer.
  • The equinox is the only time these objects will be plainly visible.
  • Days are markedly shorter now, soon autumnal equinox will be upon us.
  • Tomorrow morning is the vernal equinox.
  • The shadow should have been drawn vertically, otherwise we would be in perpetual equinox.
  • The party season doesn't stop with the spring equinox.
  • Go in the bright blaze of Autumn's equinox.
  • And I believe it's now the equinox which means less and less and less daylight.
  • During equinox, the rings cooled to the lowest temperature ever recorded.
  • It's a dumb myth that you can only stand eggs on end on the first day of spring, on the vernal equinox in March.
British Dictionary definitions for equinox


/ˈiːkwɪˌnɒks; ˈɛkwɪˌnɒks/
either of the two occasions, six months apart, when day and night are of equal length See vernal equinox, autumnal equinox
another name for equinoctial point
Word Origin
C14: from Medieval Latin equinoxium, changed from Latin aequinoctium, from aequi-equi- + nox night
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 equinox

late 14c., from Old French equinoce (12c.) or directly from Medieval Latin equinoxium "equality of night (and day)," from Latin aequinoctium "the equinoxes," from aequus "equal" (see equal (adj.)) + nox (genitive noctis) "night" (see night). The Old English translation was efnniht. Related: Equinoctial.

Online Etymology Dictionary, © 2010 Douglas Harper
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equinox in Science
  1. Either of the two points on the celestial sphere where the ecliptic (the apparent path of the Sun) crosses the celestial equator. ◇ The point at which the Sun's path crosses the celestial equator moving from south to north is called the vernal equinox. The vernal equinox marks the zero point in both the equatorial and ecliptic coordinate systems; horizontal angular distances (right ascension in the equatorial system and celestial longitude in the ecliptic system) are measured eastward from this point. The vernal equinox is also known as the first point of Aries because when first devised some 2,000 years ago this point occurred at the beginning of Aries in the zodiac. Because of the westward precession of the equinoxes, the vernal equinox is now located at the beginning of Pisces. ◇ The point at which the Sun's path crosses the celestial equator moving from north to south is called the autumnal equinox.

  2. Either of the two corresponding moments of the year when the Sun is directly above the Earth's equator. The vernal equinox occurs on March 20 or 21 and the autumnal equinox on September 22 or 23, marking the beginning of spring and autumn, respectively, in the Northern Hemisphere (and the reverse in the Southern Hemisphere). The days on which an equinox falls have about equal periods of sunlight and darkness. Compare solstice.

The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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equinox in Culture
equinox [(ee-kwuh-noks, ek-wuh-noks)]

The twice yearly times when the lengths of day and night are equal. At equinox, the sun is directly over the Earth's equator. The vernal equinox occurs about March 22 and the autumnal equinox about September 21.

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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