'stain-free' originates from Modern English as a compound of the words 'stain' and 'free'. 'Stain' comes from Old Norse, specifically the word 'steina', where the root meant 'to discolor or spot'. 'Free' comes from Old English, specifically the word 'frēo', where the root meant 'not in bondage or exempt'.

'stain' changed from Old Norse 'steina' to Middle English 'stainen' and eventually became the modern English word 'stain'. 'Free' evolved from Old English 'frēo' through Middle English into the modern English word 'free'. The compound 'stain-free' is a more recent Modern English formation combining these two words.

Initially, 'stain' primarily meant 'to smear or discolor' and 'free' meant 'not in bondage or exempt'; over time 'stain' came to be used for marks or blemishes and 'free' took the sense 'without', so the compound now means 'without stains' in both literal and extended figurative uses.