'roundworm' originates from Modern English, specifically the words 'round' and 'worm', where 'round' ultimately comes from Old French 'rond' (from Latin 'rotundus') meaning 'round' and 'worm' comes from Old English 'wyrm' meaning 'serpent, worm'.

'roundworm' changed from the combination of Middle English/Old French 'round' (from Old French 'rond') and Old English 'wyrm' (worm) and eventually became the modern English compound 'roundworm'.

Initially the components meant 'round' and 'worm' (a general term for creeping creatures); over time the compound came to be used specifically for cylindrical nematode worms, often parasitic.