Black's Law Dictionary (2nd edition)dictionaries

Equinoxes

The two periods of the year (vernal equinox about March 21st, and autumnal equinox about September 22d) when the time from the rising of the snn to its setting is equal to the time from its set-ting to its rising. See Dig. 43, 13,1, 8

Source: Black’s Law Dictionary 2nd Ed (1910)