[rey-dee-oh-soh-dee-uh m] /ˌreɪ di oʊˈsoʊ di əm/
the radioactive isotope of having an atomic mass of 24 and a half-life of 14.9 hours: used as a tracer in biochemistry.
noun, Astronomy. 1. a cosmic object or phenomenon, as a galaxy, pulsar, quasar, or the remnant of a supernova or of a galactic collision, that emits radio waves. noun 1. a celestial object, such as a supernova remnant or quasar, that is a source of radio waves
noun 1. the portion of the electromagnetic spectrum that includes radio waves. noun 1. the range of electromagnetic frequencies used in radio transmission, lying between 10 kilohertz and 300 000 megahertz
noun, Astronomy Now Rare. 1. a radio source. noun 1. a former name for radio source
noun 1. (def 8). noun 1. an installation consisting of one or more transmitters or receivers, etc, used for radiocommunications 2. a broadcasting organization