ꜣmn

The word ammonia reaches English from modern Latin ammonia, which derives from sal ammoniacus — salt of Ammon — the name given by ancient writers to the ammonium chloride salt found in deposits near the temple and oracle of the god Amun (Greek: Ammon, Latin: Ammon or Hammon) at the Siwa Oasis in the Libyan desert, west of the Nile delta. The Egyptian name of the god — Imn, conventionally vocalized as Amen or Amun — means 'the hidden one' or 'the concealed,' from the Egyptian root mn (to be hidden, concealed, enduring). Amun was the king of the gods in the New Kingdom and among the most powerful deities in the Egyptian pantheon, his great temple at Karnak the wealthiest religious institution in the ancient world. But it was the desert oracle at Siwa — where Alexander the Great famously visited in 331 BCE and was proclaimed son of Ammon — that gave chemistry its name for a gas, through the unexpected chemistry of camel urine on desert soil.

Sal ammoniacus (ammonium chloride) was found naturally occurring at Siwa in crusts on the desert floor, formed through the evaporation of urine from the camels and other animals that gathered at the oasis. The salt was collected and used medicinally and industrially in the ancient and medieval worlds: as a flux for metalworking, as a preservative, in dyeing, and in various pharmaceutical preparations. The name sal ammoniacus ('Ammonite salt,' 'salt of Ammon') recorded its geographic-religious origin — the salt of the place of Ammon's oracle. Medieval Islamic alchemists, translating and transmitting ancient chemical knowledge, knew the compound as nūshādir (Arabic) but also recorded the Latin name. When European chemists in the 17th and 18th centuries began isolating and studying the caustic gas released when sal ammoniacus was heated, they named the gas after the salt: spirit of hartshorn was one name, but ammonia, from the salt's name, was what stuck.

The gas itself — NH₃, nitrogen trihydride — was isolated and characterized by Joseph Priestley in 1774 and named by Claude Louis Berthollet in 1785, who established its composition of nitrogen and hydrogen. Berthollet retained the traditional name ammonia despite establishing the compound's chemical nature. The industrial synthesis of ammonia — the Haber-Bosch process, developed by Fritz Haber and Carl Bosch in Germany in the early 20th century — is one of the most consequential chemical achievements in history: it produces the nitrogen fertilizers that currently sustain approximately half of the world's food supply. The nitrogen in roughly half of all the protein in every human body on Earth today passed through the Haber-Bosch ammonia synthesis process. This process, and the compound it produces, bear the name of the Egyptian god Amun through the chain: Amun → Ammon → sal ammoniacus → ammonia.

The etymological path from Egyptian deity to industrial chemistry illustrates a type of linguistic transmission that bypasses cultural awareness: no chemist working with ammonia needs to know, or typically does know, that the compound's name honors the hidden god of Egyptian theology. The name traveled through Greek, Latin, medieval Arabic scholarship, and early modern European chemistry as a geographic label (salt from near Ammon's place) that was then applied to the gas derived from that salt. Amun — the king of the gods who was worshipped at Karnak in temples built from the wealth of empires, whose name means 'the concealed one' — is now hidden, appropriately, inside the word for a gas that makes your eyes water in the cleaning aisle of a supermarket.