The Collaborative International Dictionary of English v.0.48:

Equinox \E"qui*nox\, n. [OE. equinoxium, equenoxium, L.
   aequinoctium; aequus equal + nox, noctis, night: cf. F.
   ['e]quinoxe. See Equal, and Night.]
   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.             --Longfellow.
      [1913 Webster]

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

WordNet (r) 3.0 (2006):

equinox
    n 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
    2: (astronomy) either of the two celestial points at which the
       celestial equator intersects the ecliptic [syn: equinoctial
       point, equinox]

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "equinox":
   aphelion, apogee, astronomical longitude, autumnal equinox,
   celestial equator, celestial longitude, celestial meridian, circle,
   colures, ecliptic, equator, equinoctial, equinoctial circle,
   equinoctial colure, galactic longitude, geocentric longitude,
   geodetic longitude, great circle, heliocentric longitude,
   longitude, meridian, orbit, perigee, perihelion, period,
   small circle, solstice, solstitial colure, summer solstice,
   trajectory, vernal equinox, winter solstice, zodiac, zone