From Longman Dictionary of Contemporary Englishcesiumce‧si‧um /ˈsiːziəm/ noun [uncountable] the American spelling of caesium
Examples from the Corpus
cesium• The definition of a second has since officially been the time it takes a cesium atom to make 9,192,631,770 vibrations.• During irradiation, food is exposed to gamma rays from sources such as cobalt 60 or cesium 137. 