'equinox' originates from Latin, specifically the word 'aequinoctium,' where 'aequi-' meant 'equal' and 'nox' meant 'night.'

'aequinoctium' transformed into the Old French word 'equinoxe,' and eventually became the modern English word 'equinox' through Middle English.

Initially, it meant 'equal night,' referring to the time when day and night are of equal length, and this meaning has largely remained the same in modern usage.