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

Winter’s meteorological end is Friday, February 28, 2025 while the astronomical end is on Thursday, March 20, 2025, at the start of the spring equinox, according to the Old Farmer’s Almanac. —Cailey Gleeson, Journal Sentinel, 11 Dec. 2024

The solstice marks the first day of winter, which lasts until the spring equinox March 20, 2025. —Tiffany Acosta, The Arizona Republic, 10 Dec. 2024

As the calendar moves away from the frantic sports equinox, the NBA stands to gain more attention for its early season action with its annual trip to Mexico. —Jason Clinkscales, Sportico.com, 2 Nov. 2024

Why the full moon is called hunter’s moon The hunter’s moon is the first full moon after the autumnal equinox, which occurred on September 22 this year. —Gina Park and Ashley Strickland, CNN, 16 Oct. 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