COBALT 60(noun)Did you mean?Synonyms RhymesDefinitions There is 1 meaning of the phrase Cobalt 60. Cobalt 60 - as a noun A radioactive isotope of cobalt with mass number 60; a source of exceptionally intense gamma rays; used in radiation therapy A-Z Proximitiescobaea10cobaeas11cobalamin15cobalamins16cobalt10 Cobalt 60 cobaltic14cobaltiferous20cobaltine13cobaltines14cobaltite13