noun

equinox

/ˈɛkwɪnɒks/ · say it: EK·wuh·noks

a day when day and night are of equal length

In more detail

1. (noun) either of the two times each year when day and night are approximately equal in length, occurring around March 21 (spring equinox) and September 23 (autumn equinox)

2. (noun) the moment when the sun crosses the equator, making day and night of equal duration

Examples

1. The spring equinox marks the beginning of spring in the Northern Hemisphere.
2. On the equinox, the sun rises and sets at approximately the same time everywhere on Earth.

How to use equinox

Equinox is a technical term used in astronomy and everyday contexts to refer to one of two precise moments in the year when day and night have approximately equal length. It is more specific and scientific than colloquial alternatives and is commonly used in calendars, weather discussions, and formal astronomical contexts. The word is neutral and carries no emotional connotation.

Common phrases

spring equinox
autumn equinox
vernal equinox
autumnal equinox
at the equinox

Opposites

solstice

Word family

equinoctial

A common mistake

Learners sometimes confuse equinox with solstice, which refers to the longest or shortest day of the year rather than when day and night are equal.

Learn it for good

Save this word in WordVale and it comes back for review right before you'd forget it — with pronunciation, real examples, and optional translations. One purchase, no subscription.

Get WordValeFREE 7-DAY TRIAL · iPHONE & iPAD