potassiumPronunciation: /pəˈtasɪəm/Translate potassium | into French | into German | into Italian | into Spanish Definition of potassium noun [mass noun] the chemical element of atomic number 19, a soft silvery-white reactive metal of the alkali-metal group. (Symbol: K)Derivatives potassic adjective ( Mineralogy)Origin: early 19th century: from potash (earlier potass, from French potasse) + -iumpotassium in other Oxford dictionaries Definition of potassium in the US English dictionary