equinoctial

1. Relating to an equinox.
2. Relating to the celestial equator.

1. A violent storm of wind and rain occurring at or near the time of the equinox.
2. See celestial equator.

[Middle English equinoxial, from Old French, from Latin aequinoctiālis, from aequinoctium, equinox. See equinox.]

Relating to an equinox, i.e. one of the two points in the year when Earth's axis is perpendicular to the direction of the Sun, making day and night equal in length. For equinoctial year see year.

The noun has one meaning:

Meaning #1: the great circle on the celestial sphere midway between the celestial poles
  Synonyms: celestial equator, equinoctial circle, equinoctial line

The adjective equinoctial has 2 meanings:

Meaning #1: relating to the vicinity of the equator
  Pertains to noun: equator (meaning #1)

Meaning #2: relating to an equinox (when the lengths or night and day are equal)
  Pertains to noun: equinox (meaning #1)