'postdiluvial' originates from Latin, specifically the elements 'post' and 'diluvium', where 'post' meant 'after' and 'diluvium' meant 'flood'.

'postdiluvial' developed from Late Latin 'postdiluvialis' and entered English via Medieval/early modern forms such as 'postdiluvian', eventually appearing in English as 'postdiluvial'.

Initially it meant 'relating to the period after the Flood (biblical)', and over time it has retained that meaning while also being used more generally in older geological literature to mean 'after a large flood'.