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 fall equinox arrived last month and Ohio's fall foliage scene is in full swing, but the snow will start falling before too long. —Mariyam Muhammad, Cincinnati Enquirer, 17 Oct. 2025

But given the time of year, just past the recent autumn equinox, even a small bump in activity could have a bigger impact and boost the chances of more widespread auroras this weekend. —Daisy Dobrijevic, Space.com, 10 Oct. 2025

The October supermoon happens to be the 2025 Harvest moon, the full moon closest to the autumn equinox, which rises roughly at the same time for several nights and provides more moonlight than usual. —Callum Sutherland, Time, 6 Oct. 2025

Set during the fall equinox of 1999, the film follows four friends who gather at an isolated cabin to perform a witchcraft initiation. —Naman Ramachandran, Variety, 6 Oct. 2025

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

Rhymes for equinox

• aftershocks
• chatterbox
• goldilocks
• hollyhocks
• interlocks
• orthodox
• paradox
• tomahawks
• balks
• blocks
• blocs
• box

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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