'earthworm' originates from Old English, specifically the words 'eorþe' meaning 'earth' and 'wyrm' meaning 'worm'.

'eorþe wyrm' transformed into the Middle English word 'ertheworm', and eventually became the modern English word 'earthworm'.

Initially, it meant 'a worm living in the earth', and this meaning has largely remained the same in modern usage.