1. 二分时刻，昼夜平分日（指春分或秋分）
An equinox is one of the two days in the year when day and night are of equal length.

1. (astronomy) either of the two celestial points at which the celestial equator intersects the ecliptic

Synonym: equinoctial point

2. 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