equi·​nox | \ ˈē-kwə-ˌnäks How to pronounce equinox (audio) , ˈe- How to pronounce equinox (audio) \

Definition of equinox

1 : either of the two points on the celestial sphere where the celestial equator intersects the ecliptic
2 : either of the two times each year (as about March 21 and September 23) when the sun crosses the equator and day and night are everywhere on earth of approximately equal length

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Equinox and the Seasons

Equinox descends from aequus, the Latin word for "equal," and nox, the Latin word for "night"—a fitting history for a word that describes days of the year when the daytime and nighttime are equal in length. In the northern hemisphere, the vernal equinox marks the first day of spring and occurs when the sun moves north across the equator. (Vernal comes from the Latin word ver, meaning "spring.") The autumnal equinox marks the first day of autumn in the northern hemisphere and occurs when the sun crosses the equator going south. In contrast, a solstice is either of the two moments in the year when the sun's apparent path is farthest north or south from the equator.

Examples of equinox in a Sentence

Recent Examples on the Web The Persian New Year, on the vernal equinox, lasts for 13 days. New York Times, "To-Go Meals for Sizdeh Beder," 22 Mar. 2021 The sun rises due east and sets due west (more on the equinox, coming soon). Washington Post, "D.C.-area forecast: Final showers exit quick this morning, then another sunny stretch gets underway," 19 Mar. 2021 Nowruz is celebrated on the spring equinox, which is Saturday, March 20. Megan Marples, CNN, "Celebrate Persian New Year with green recipes and spring cleaning," 19 Mar. 2021 The vernal equinox is Saturday marking the start of spring. Dallas News, "A pleasant weekend ahead," 19 Mar. 2021 Per the agreement in the Council of Trent in 1563, the new year would begin on January 1 instead of April 1, around the spring equinox. Tom Sater, CNN, "It's no joke -- thunder wakes the peepers and brings good crops of corn and hay," 31 Mar. 2021 This heightened displays coincided with the spring or vernal equinox, which occurred at 09:37 Universal Time on Saturday, 20 March, 2021. Jamie Carter, Forbes, "Strong Auroras Likely All Weekend In Northern US States As Geomagnetic Storm Strikes On Equinox," 20 Mar. 2021 Perhaps the vernal equinox on Saturday will give you time to reflect upon everything that’s happened since the last one. BostonGlobe.com, "Spring comes bounding into view," 19 Mar. 2021 But fear not, the spring equinox on Saturday ushers in a much more tranquil weekend with lots of sun and warmer temperatures to enjoy the daffodils that seem to be popping up everywhere. Washington Post, "D.C.-area forecast: Wet today and stormy tonight, then very blustery on Friday," 18 Mar. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'equinox.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of equinox

14th century, in the meaning defined at sense 1

History and Etymology for equinox

Middle English, from Anglo-French or Medieval Latin; Anglo-French equinocce, from Medieval Latin equinoxium, alteration of Latin aequinoctium, from aequi- equi- + noct-, nox night — more at night

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Time Traveler for equinox

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The first known use of equinox was in the 14th century

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Last Updated

6 May 2021

Cite this Entry

“Equinox.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equinox. Accessed 9 May. 2021.

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More Definitions for equinox



English Language Learners Definition of equinox

: a day when day and night are the same length


equi·​nox | \ ˈē-kwə-ˌnäks How to pronounce equinox (audio) , ˈe-kwə- \

Kids Definition of equinox

: either of the two times each year (as in spring around March 21 and in fall around September 23) when the sun's center crosses the equator and day and night are everywhere of equal length

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More from Merriam-Webster on equinox

Nglish: Translation of equinox for Spanish Speakers

Britannica English: Translation of equinox for Arabic Speakers

Britannica.com: Encyclopedia article about equinox

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