High Quality Content by WIKIPEDIA articles! Niter (AmE) or nitre (BrE) is the mineral form of potassium nitrate, KNO3, also known as saltpeter (AmE) or saltpetre (BrE). Historically, the term "niter" – cognate with "natrium", a Latin word for sodium – has been very vaguely defined, and it has been applied to a variety of other minerals and chemical compounds, including sodium nitrate (also "soda niter", "cubic niter", or nitratite), sodium carbonate and potassium carbonate.