potassium nitrate; niter; a white crystalline substance, kno3, having a cooling saline taste, obtained by leaching from certain soils in which it is produced by the process of nitrification (see nitrification, 2). it is a strong oxidizer, is the chief constituent of gunpowder, and is also used as an antiseptic in curing meat, and in medicine as a diuretic, diaphoretic, and refrigerant.