'protein-free' originates from a modern English compound of 'protein' and 'free'; 'protein' ultimately comes from Greek 'proteios' (via 19th-century scientific coinage 'protein'), and 'free' comes from Old English 'frēo'.

'protein' was coined in the early 19th century from Neo-Latin/French scientific usage based on Greek 'proteios' (related to 'protos' meaning 'first'), while 'free' developed from Old English 'frēo' into Middle and then Modern English; the compound 'protein-free' arose in modern English by combining these elements to describe absence of protein.

Originally the Greek root 'proteios' meant 'of first importance'; it later gave its name to the biological substance 'protein' in the 19th century. 'Free' has long meant 'not containing or not subject to' and together the compound now means 'without protein'.