equinox

• æquinox (obsolete)

From Old French equinoce (French équinoxe), from Medieval Latin equinoxium, from Latin aequinoctium, from aequus (“equal”) + nox (“night”). Replaced Old English efenniht (Modern English evennight).

• (Received Pronunciation) IPA^(key): /ˈɛkwɪˌnoks/, /ˈiːkwɪˌnɒks/
• (General American) IPA^(key): /ˈiːkwəˌnɑːks/

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equinox (plural equinoxes or equinoctes)

1. (astronomy) The intersection of the apparent path of the sun in the sky (the ecliptic) with the celestial equator.
2. One of the two days on which this intersection occurs each year: (for the Northern hemisphere) March 20 or 21 in the spring and September 22 or 23 in the autumn.
   • 2005, Clive L. N. Ruggles, Ancient Astronomy: An Encyclopedia of Cosmologies and Myth

     Since it gets light before the sun rises and remains light after the sun sets, the actual period of darkness at the equinox will be substantially less than twelve hours, the exact amount depending on latitude and how one defines the boundary between twilight and night.

• autumn equinox
• autumnal equinox
• March equinox
• September equinox
• spring equinox
• vernal equinox

• solstice

• (adj, archaic) equinoxial
• northward equinox
• precession of the equinoxes
• southward equinox

• (adj) equinoctial, equinoctal
• interequinoctial