'ammonium-free' is a compound of 'ammonium' and 'free'. 'Ammonium' originates from Neo-Latin 'ammonium', ultimately from Latin/Medieval Latin 'sal ammoniacus' (salt of Ammon), where 'Ammon' referred to the Egyptian deity Ammon; 'free' originates from Old English 'frēo', meaning 'not in bondage' or 'without'.

'ammonium' developed from names for salts associated with the temple of Ammon (Latin 'sal ammoniacus') into the chemical term 'ammonia' and later the ionic form name 'ammonium' in modern chemistry; 'free' evolved from Old English 'frēo' → Middle English 'free' to the modern adjective 'free'. The compound 'ammonium-free' is a modern product-label/technical formation combining the chemical noun with 'free'.

Originally 'ammonium' referred to salts associated with the oracle/temple of Ammon; over time it came to denote the chemical species (ammonia, then the ammonium ion NH4+). 'Free' originally meant 'not in bondage' and extended to mean 'without' or 'lacking' in compounds like this; together the compound now means 'without ammonium'.