'ammonia-free' originates from English, specifically a compound of 'ammonia' and 'free', where 'ammonia' ultimately comes from Latin/Medieval Latin 'ammonia' (from 'sal ammoniac', 'salt of Ammon') and 'free' comes from Old English 'frēo' meaning 'not bound or exempt'.

'ammonia' changed from Latin/Medieval Latin terms related to 'sal ammoniac' (named for the Egyptian god Ammon) into Modern Latin 'ammonia' and then into English 'ammonia'; 'free' evolved from Old English 'frēo' through Middle English into modern 'free'. The compound 'ammonia-free' was formed in modern English by joining these elements to mean 'without ammonia'.

Initially, 'ammonia' referred to salts associated with Ammon ('salt of Ammon') and later to the chemical NH3; 'free' originally meant 'exempt' or 'not bound'. Over time the compound came to mean 'without ammonia' in product and chemical contexts.