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 That’s why this equinox supermoon is also being called a super worm moon. Andrew Fazekas, National Geographic, "See the first supermoon on the spring equinox in 19 years," 19 Mar. 2019 Vehicle is a gold or silver equinox with body damage. James Burky, The Denver Post, "One person shot in alleged robbery in Arvada; police looking for suspect," 18 Dec. 2019 Solstices occur twice a year, one in the winter and once in the summer, while the equinoxes occur once in the spring and once in the fall. Madison Roberts, PEOPLE.com, "The Shortest Day of the Year is Almost Here—Everything to Know About the Winter Solstice," 16 Dec. 2019 The autumnal #equinox officially occurred at 12:50am. oregonlive, "Portland metro Monday weather: First day of fall brings sun, moderate temps," 23 Sep. 2019 Fall actually began at 3:50 Monday morning, the moment of the autumnal equinox. Scott Dance, baltimoresun.com, "Maryland weather: Today is the first day of fall, but more summer-like heat is in the forecast," 23 Sep. 2019 The equinox occurs precisely when the Sun’s center passes through this line. Patrick May, The Mercury News, "Pumpkin patches, corn mazes and colorful leaves: Fun facts to greet the first day of fall," 20 Sep. 2019 The autumn equinox will occur at 12:50 a.m. on Sept. 23. Gary Robbins, San Diego Union-Tribune, "San Diego weather will turn cool this week -- but wildfire conditions tick up," 16 Sep. 2019 Around the date of the autumnal equinox though, the moon rises only 20 minutes later each night. Mike Lynch, Twin Cities, "Mike Lynch: The harvest moon is shining bright this week," 15 Sep. 2019

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

5 Feb 2020

Cite this Entry

“Equinox.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equinox. Accessed 17 Feb. 2020.

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More Definitions for equinox


How to pronounce equinox (audio) How to pronounce equinox (audio)

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

Rhyming Dictionary: Words that rhyme with equinox

Spanish Central: Translation of 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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