'equinoctial' originates from Latin, specifically the word 'aequinoctialis,' where 'aequi-' meant 'equal' and 'noctis' meant 'night.'

'aequinoctialis' transformed into the Old French word 'equinoctial,' and eventually became the modern English word 'equinoctial.'

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