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

'agnathan' was formed from New Latin 'Agnatha' (used in 19th-century taxonomy) and entered English scientific usage as a noun/adjective for members of that group; the English form derives directly from the taxonomic New Latin.

Initially it meant 'without jaws' (literal component meaning), and over time it came to denote specifically 'a jawless vertebrate' or a member of the taxonomic group Agnatha.