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

In honor of the new collection—and the summer equinox—Kroger is celebrating with a major giveaway: 92,000 pints of free ice cream on June 20, 2025. —Abigail Wilt, Southern Living, 12 June 2025

The date of the holiday changes annually and is determined by the first full moon on or after the March equinox. —Cody Godwin, USA Today, 17 Apr. 2025

Life advice Angela Hsieh/NPR Today is the spring equinox. —Brittney Melton, NPR, 20 Mar. 2025

Like clockwork, astronomical spring starts on the vernal equinox. —John Walkup, Forbes.com, 23 Apr. 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