1.  equinox(n = noun.time) - 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;
is a kind of cosmic time
has particulars: march equinox, spring equinox, vernal equinox, autumnal equinox, fall equinox, september equinox
Derived form adjective equinoctial₂

2.  equinox(n = noun.location) equinoctial point - (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic;
is a kind of celestial point
has particulars: vernal equinox, autumnal equinox

1.  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. [1913 Webster]
"When descends on the Atlantic
The gigantic
Stormwind of the equinox." [1913 Webster]

2.  Equinoctial wind or storm. Dryden. [1913 Webster]

equinox, n.
1 the time or date (twice each year) at which the sun crosses the celestial equator, when day and night are of equal length.
2 = equinoctial point.

Idiom:
autumn (or autumnal) equinox about 22 Sept. spring (or vernal) equinox about 20 March.

Etymology:
ME f. OF equinoxe or med.L equinoxium for L aequinoctium (as EQUI-, nox noctis night)

autumnal equinox, fall equinox, march equinox, september equinox, spring equinox, vernal equinox