'Devonian' originates from English, specifically the place name 'Devon' combined with the adjectival suffix '-ian', where 'Devon' ultimately derives from the name of the Celtic tribe 'Dumnonii' (Latin 'Dumnonia').

'Devonian' was coined in the 19th century as the name for the geological period after the county name 'Devon'. The place name 'Devon' evolved in English from Old English forms and ultimately from Latin 'Dumnonia', itself from the tribal name 'Dumnonii'.

Initially it meant 'of or relating to Devon (the place)', but in the 19th century it came to denote the geological period now called the Devonian; both senses continue in modern use.