[equi.nox] n [ME, fr. MF or ML; MF equinoxe, fr. ML equinoxium, alter. of L aequinoctium, fr. aequi- equi- + noct-, nox night--more at night] (14c) 1: either of the two points on the celestial sphere where the celestial equator intersects the ecliptic
2: either of the two times each year (as about March 21 and September 23) when the sun crosses the equator and day and night are everywhere of equal length