"Old-fashioned term for ammonium chloride", Middle English: from Latin sal ammoniacus 'salt of Ammon' (see ammoniacal).[sal ammoniac etymology, sal ammoniac origin, 英语词源]
"Of or containing ammonia", Mid 18th century: from Middle English ammoniac, via Old French from Latin ammoniacus. This represented the Greek word ammōniakos 'of Ammon', used as a name for the salt and gum obtained near the temple of Jupiter Ammon at Siwa in Egypt. Compare with sal ammoniac.