'archaean' originates from New Latin, specifically the word 'Archean', where the Greek root 'arkhaios' meant 'ancient' (from 'arkhē' meaning 'beginning, origin').

'archaean' changed from the Greek word 'arkhaios' into a Latinized New Latin form 'Archean' used in scientific contexts, and eventually became the modern English adjective and noun 'archaean'.

Initially, it meant 'ancient' in a general sense, but over time it evolved into its current specialized meaning of 'relating specifically to the Archean eon or things from that eon'.