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radioactive (adj.)

1898, of an atomic nucleus, "capable of spontaneous nuclear decay releasing ionizing emissions," from French radio-actif, coined by Pierre and Marie Curie from radio-, combining form of Latin radius "ray" (see radius) + actif "active" (see active). Of processes, etc., "involving or produced by radioactivity," by 1903.

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Definitions of radioactive from WordNet

radioactive (adj.)
exhibiting or caused by radioactivity;
radioactive decay
radioactive isotope
radioactive fallout
From wordnet.princeton.edu