RADIOACTIVITY Meaning of RADIOACTIVITY in English radioactivity BrE AmE ˌreɪd i‿əʊ æk ˈtɪv ət i -ɪt i AmE \ -oʊ æk ˈtɪv ət̬ i Longman Pronunciation English Dictionary. Английский словарь произношений Longman. 2012