'threadworm' originates from Modern English, specifically the compound of the words 'thread' and 'worm', where 'thread' meant 'a thin strand' and 'worm' meant 'an invertebrate animal or creeping creature'.

'thread' comes from Old English 'þræd' (Middle English 'thred'), and 'worm' comes from Old English 'wyrm'; the compound 'threadworm' developed in English by combining these elements to describe a thin, thread-like worm.

Initially, it meant 'a thin, thread-like worm' in a general sense, but over time it has come to refer specifically (especially in British usage) to the intestinal parasite 'Enterobius vermicularis' (pinworm).