Other forms: equinoxes
An equinox is one of the two days when day and night are equal. The spring equinox, autumn equinox, around the equinox.
It is the moment the sun crosses the celestial equator, in March and September, and it is the same instant everywhere on earth. Day and night are not exactly equal on it — refraction and the size of the sun's disc add a few minutes of daylight. Note that the Latin means equal night.
1nounequinoxOne of the two days when day and night are about equal.
“At the spring equinox, the sun rises almost exactly in the east.”
equinox is an astronomical event.
Latin aequinoctium is aequus, equal, plus nox, night. Equal and nocturnal come from the two halves.
Proto-Indo-European
*nókʷts — night
Latin
aequinoctium — equinox
Medieval Latin
ēquinoxium
Old French
equinoce
Middle English
equinox
English, today
equinox
Built from
From Middle English equinox, equinoxe, equynox (“one of the two periods in the year when the day and night are of equal length, equinox; either the zodiac sign Aries or Libra, in which the sun crosses the celestial equator”), from Old French equinoce, equinoxe (modern French équinoxe), or from its etymon Medieval Latin ēquinoxium, ēquinoctium, from Latin aequinoctium (“equinox”), from aequus (“equal”) + nox (“night”) (ultimately derived from Proto-Indo-European nókʷts (“night”)) + -ium. The Latin word, ultimately adopted in Middle English and modern English, displaced Old English efnniht (modern English evennight). The rare alternative plural form equinoctes treats equinox as if it were a Latin word; the plural of Latin nox (“night”) is noctēs.
Etymology from Wiktionary, CC BY-SA