Pertaining to the equinoxes; designating an equal length of day and night; as the equinoctial line.

Pertaining to the regions or climate of the equinoctial line or equator; in or near that line; as equinoctial heat; an equinoctial sun; equinoctial wind.

Pertaining to the time when the sun enters the equinoctial points; as an equinoctial gale or storm, which happens at or near the equinox, in any part of the world.

Equinoctial flowers, flowers that open at a regular, stated hour.

In astronomy, a great circle of the sphere, under which the equator moves in its diurnal course. This should not be confounded with the equator, as there is a difference between them; the equator being movable, and the equinoctial immovable; the equator being drawn about the convex surface of the sphere, and the equinoctial on the concave surface of the magnus orbis. These words however are often confounded. When the sun, in its course through the ecliptic, comes to this circle, it makes equal days and nights in all parts of the globe. The equinoctial then is the circle which the sun describes, or appears to describe, at the time the days and nights are of equal lengthabout the 21st of March and 23d of September. Equinoctial points, are the two points wherein the equator and ecliptic intersect each other; the one, being in the first point of Aries, is called the vernal point or equinox; the other, in the first point of Libra, the autumnal point or equinox. Equinoctial dial, is that whose plane lies parallel to the equinoctial.