'tumour-free' originates from Modern English, specifically the compound of 'tumour' (from Latin 'tumor') and 'free' (from Old English 'freo'), where 'tumor' meant 'a swelling' and 'free' meant 'not subject to or affected by'.

'tumour' changed from Latin 'tumor' into Old French and Middle English forms (e.g. 'tumor/tumour') and became the modern English 'tumour'; 'free' developed from Old English 'freo' and remained the word 'free' in Modern English. The compound 'tumour-free' is a relatively recent productive modern English formation combining these elements.

Initially 'tumor' meant 'a swelling'; over time it came to mean an abnormal growth (benign or malignant). 'tumour-free' thus originally literally meant 'without swelling' and evolved to the current medical sense of 'without detectable tumour'.