'agnathan' originates from New Latin, specifically the taxonomic name 'Agnatha', ultimately from Ancient Greek 'agnathos', where 'a-' meant 'without' and 'gnathos' meant 'jaw'.

'agnathan' was formed from the taxonomic name 'Agnatha' (coined in modern scientific classification) and entered English as the adjective/noun 'agnathan' to denote members of that group (jawless fishes).

Initially it meant 'without jaws' (the literal Greek sense), and over time it became established as the term for the jawless fishes; the core meaning has been retained.