'archaeal' originates from New Latin 'Archaea', ultimately from Greek 'arkhaîos', where 'arkhaios' meant 'ancient' or 'primitive'.

'archaeal' was formed in modern scientific English by taking the taxonomic name 'Archaea' (coined in the late 20th century for a distinct domain of life) and adding the adjectival suffix '-al' to produce the adjective 'archaeal'.

Initially the root meant 'ancient'; over time it became the taxonomic name for a domain of microorganisms, and 'archaeal' came to mean 'relating to Archaea' rather than simply 'ancient'.