these classical names are direct derivatives of Latin (ver = spring and autumnus = autumn). These names are based on the seasons, and can be ambiguous since seasons of the northern hemisphere and southern hemisphere are opposites, and the vernal equinox of one hemisphere is the autumnal equinox of the other.
An equinox occurs twice a year, around 20 March and 22 September. The word itself has several related definitions. The oldest meaning is the day when daytime and night are of approximately equal duration.[2] The word equinox comes from this definition, derived from the Latin aequus (equal) and nox (night). The equinox is not exactly the same as the day when period of daytime and night are of equal length for two reasons. Firstly, sunrise, which begins daytime, occurs when the top of the Sun's disk rises above the eastern horizon. At that instant, the disk's center is still below the horizon. Secondly, Earth's atmosphere refracts sunlight. As a result, an observer sees daylight before the first glimpse of the Sun's disk above the horizon.