'gnathostome' originates from New Latin and ultimately from Greek, specifically the Greek word 'gnathóstomos' (γναθοστόμος), where 'gnath-' meant 'jaw' and 'stoma' meant 'mouth'.

'gnathostome' changed from New Latin taxonomic usage 'Gnathostomata' (used to name the group) which itself was coined from Greek 'gnathóstomos'; through scientific Latin it entered modern English as 'gnathostome' (singular) and 'gnathostomes' (plural).

Initially it literally meant 'jaw‑mouthed' in Greek, but over time it evolved into its current biological sense of 'a member of the jawed vertebrates (Gnathostomata)'.