From Longman Dictionary of Contemporary Englishequinoxeq‧ui‧nox /ˈiːkwənɒks, ˈe- $ -nɑːks/ noun [countable] HEGone of the two times in a year when night and day are of equal length → solstice the spring equinox
Examples from the Corpus
equinox• There arc four seasons, or rather four solar points of the year, the solstices and equinoxes.• Only during the time of the spring and autumn equinoxes do our aquariums have a tropical day.• Dominic knows that in the 1960s the equinox had progressed to Aquarius.• The equinox had surely passed already, and perhaps the solstice was approaching.Origin equinox (1300-1400) French équinoxe, from Latin aequinoctium, from aequi- (EQUI-) + nox “night” 