Equinox

n. either of two times in a year when the sun crosses the celestial equator; either of the two points at which the sun's path intersects with the celestial equator

In astronomy, equinox can have two meanings:The moment when the Sun is positioned directly over the Earth's equator and, by extension, the apparent position of the Sun at that moment - see below.A moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system - see Equinox (celestial coordinates)
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Noun
1. either of two times of the year when the sun crosses the plane of the earth's equator and day and night are of equal length
(hypernym) cosmic time
(hyponym) vernal equinox, March equinox, spring equinox
2. (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic
(synonym) equinoctial point
(hypernym) celestial point
(hyponym) vernal equinox
(classification) astronomy, uranology

adj. equinoctial, pertaining of an instance in which the Sun crosses the Earth's equator

(n.)
The time when the sun enters one of the equinoctial points, that is, about March 21 and September 22. See Autumnal equinox, Vernal equinox, under Autumnal and Vernal.
  

(n.)
Equinoctial wind or storm.