Niter (US) or nitre (UK)'s the mineral form of potassium nitrate, KNO3, also known as saltpeter (US) or saltpetre (UK). Historically, the term "nitre" – cognate with "natrium", a Latin word for sodium – has been very vaguely defined, and it's been applied to a variety of other minerals and chemical compounds, including sodium nitrate (also "soda nitre" or "cubic nitre"), sodium carbonate and potassium carbonate. This article's about the mineral form of potassium nitrate, which's the… (More on Niter)