'earthworm' originates from Old English, specifically the compound of 'eorþe' and 'wyrm', where 'eorþe' meant 'ground, soil' and 'wyrm' meant 'creeping thing' or 'serpent'.

'earth' (from Old English 'eorþe') and 'worm' (from Old English 'wyrm') appeared in Middle English in forms like 'erthe worm' and later became the modern compound 'earthworm'.

Initially, it meant 'a creeping thing of the earth' more generally, but over time it became specialized to refer to the soil-dwelling annelid now called an 'earthworm'.