equinox

noun

equi·​nox ˈē-kwə-ˌnäks  ˈe- 

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" 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 autumnal equinox is one of two points in Earth’s orbit where the sun creates equal periods of daytime and nighttime across the globe. —Michael Roston, New York Times, 1 Jan. 2025

The Sumerians, who lived in the region that is now modern-day Iraq, celebrated the beginning of the year during the spring equinox in late March, according to the History Channel. —Brandi D. Addison, The Arizona Republic, 31 Dec. 2024

The equinox is known as the astronomical start of the season, but there is another method used to measure the change in seasons. —Joyce Orlando, The Tennessean, 22 Sep. 2024

However, the geomagnetic storms that produce them tend to be more frequent and intense around the equinoxes. —Jamie Carter, Forbes, 31 Dec. 2024

Word History

Etymology

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

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Kids Definition

equinox

noun

equi·​nox ˈē-kwə-ˌnäks  ˈek-wə- 

: 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

Etymology

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