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

Keep scrolling for more

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 first day of astronomical autumn, or the fall equinox, will be Sept. 22 at 8:30 a.m. CDT. Leigh Morgan, al, "Summer solstice 2020: It’s the longest day of the year, sort of," 20 June 2020 During Saturn’s equinox, when the rings’ plane aligns with the sun, these tiny perturbations cast mesmerizing shadows on the planet. 11. Jennifer Leman, Popular Mechanics, "Every Moon in Our Solar System, Ranked," 7 Apr. 2020 There are two reasons, according to Space.com, that the vernal equinox is coming a bit early this year: Daylight Savings Time and the leap year having added an extra day to February. Fox News, "Vernal equinox brings earliest spring to US in 124 years," 20 Mar. 2020 Just a few weeks shy of the spring equinox, New York City was enjoying nearly perfect 70-degree weather. Keyaira Kelly, Essence, "How To Navigate the Pandemic When You And Your Partner Have Different Coping Styles," 17 Apr. 2020 In different cultures spring equinox is a time of rebirth and new beginnings. Isabel Garcia, House Beautiful, "The Earliest Spring in More Than a Century Is Happening This Week," 16 Mar. 2020 Millions of individuals worldwide gather with family to mark the vernal equinox, which Uyghurs consider their New Year. Sarah Matusek, The Christian Science Monitor, "One American Uyghur’s vow: ‘I should’ve gone public a long time ago.’," 1 Apr. 2020 The spring equinox always falls on March 19, 20 or 21. Leigh Morgan, al, "Spring equinox 2020: It’s earliest astronomical spring in 124 years," 19 Mar. 2020 During the equinox, the sun moves north along the celestial equator. Lisa Stardust, Teen Vogue, "How to Celebrate the Spring Equinox 2020 By Zodiac Sign," 19 Mar. 2020

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.

See More

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

Keep scrolling for more

Learn More about equinox

Time Traveler for equinox

Time Traveler

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

See more words from the same century

Listen to Our Podcast about equinox

Statistics for equinox

Last Updated

4 Jul 2020

Cite this Entry

“Equinox.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equinox. Accessed 8 Aug. 2020.

Keep scrolling for more

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

Keep scrolling for more

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

Comments on equinox

What made you want to look up equinox? Please tell us where you read or heard it (including the quote, if possible).


Test Your Vocabulary

Original Meanings Quiz

  • rembrandt painting a young scholar and his tutor
  • Which of the following is the earliest known sense of the word awe?
Spell It

Can you spell these 10 commonly misspelled words?

Bee Cubed

Test Your Knowledge - and learn some interesting things along the way.

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!