natron n.

c. 1400, "native sodium carbonate" (a sense now obsolete), from Old French nitre (13c.), from Latin nitrum, from Greek nitron, which is possibly of Eastern origin (compare Hebrew nether "carbonate of soda;" Egyptian ntr). Originally a word for native soda, but also associated since the Middle Ages with saltpeter (potassium nitrate) for obscure reasons; this became the predominant sense by late 16c.

metallic alkaline element, 1807, coined by English chemist Humphry Davy from soda + -ium. So called because the element was isolated from caustic soda (sodium hydroxide). The chemical symbol Na is from natrium, the name for the element that had been proposed by Berzelius and coined from natron, a name of a type of soda.