Meaning of RADIOACTIVE in English

ra ‧ di ‧ o ‧ ac ‧ tive /ˌreɪdiəʊˈæktɪv◂ $ -dioʊ-/ BrE AmE adjective

a radioactive substance is dangerous because it contains ↑ radiation (=a form of energy that can harm living things) :

the problem of how to dispose of radioactive waste

a consignment of highly radioactive plutonium

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.