Niter, or nitre ("chiefly British variant"), is the mineral form of potassium nitrate, KNO₃, also known as saltpeter or saltpetre. Historically, the term "niter" was not well differentiated from natron, both of which have been very vaguely defined but generally refer to compounds of sodium or potassium joined with carbonate or nitrate ions. Three related minerals are soda niter (sodium nitrate), ammonia niter (ammonium nitrate), and strontium nitrate. Niter was used to refer specifically to nitrated salts known as various types of saltpeter (only nitrated salts were good for making gunpowder) by the time niter and its derivative nitric acid were first used to name the element nitrogen, in 1790.