: either of the two points on the celestial sphere where the celestial equator intersects the ecliptic
: 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

Did you know?

Equinox and the Seasons

Equinox descends from aequus, the Latin word for "equal" or "even," 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 sanctuary will be officially dedicated Sept. 20 — just two days before another celestial event, the autumnal equinox, when day and night are equally long. Detroit Free Press, 8 Apr. 2024 That year, France implemented the Gregorian calendar, shifting the start of the New Year from the spring equinox, which usually falls around April 1, to January 1. Aliza Chasan, CBS News, 1 Apr. 2024 Here in the northern hemisphere, this year’s spring equinox took place on March 19, wrapping up the winter and heralding in the rejuvenating vibes of springtime. Nina Kahn, Travel + Leisure, 21 Mar. 2024 The equinox ushers you into unabashed introspection. USA TODAY, 19 Mar. 2024 Astronomical spring officially begins with the spring equinox, which takes place on Tuesday, March 19 this year. Claire Reid, Journal Sentinel, 18 Mar. 2024 There are plenty of spring equinox rituals and traditions to consider. Marina Johnson, The Courier-Journal, 16 Mar. 2024 The spring equinox, which marks the official start of spring, is on Tuesday, March 19. Hanh Truong, Sacramento Bee, 7 Mar. 2024 Over the last few years, the spring equinox has landed on March 20. Victoria Moorwood, The Enquirer, 26 Feb. 2024

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'equinox.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


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

First Known Use

14th century, in the meaning defined at sense 1

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


Dictionary Entries Near equinox

Cite this Entry

“Equinox.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/equinox. Accessed 20 Apr. 2024.

Kids Definition


: either of the two times each year about March 21 and September 23 when the sun appears overhead at the equator and day and night are everywhere of equal length

Latin equinoxium (same meaning), derived from earlier Latin aequi- "equal" and noct-, nox "night" — related to nocturnal

More from Merriam-Webster on equinox

Last Updated: - Updated example sentences
Love words? Need even more definitions?

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