radio-

1. a combining form with the meanings “dealing with radiant energy” (radiometer), “employing or dealing with radio waves” (radioacoustics; radiolocation; radiotelephone), “emitting rays as a result of the breakup of atomic nuclei” (radioactive; radiocarbon), “characterized by, employing or dealing with such rays” (radiography; radiopaque; radiotherapy).

combining form

1. denoting radio, broadcasting, or radio frequencyradiogram
2. indicating radioactivity or radiationradiochemistry; radiolucent
3. indicating a radioactive isotope or substanceradioactinium; radiothorium; radioelement

word-forming element meaning 1. “ray, ray-like” (see radius); 2. “radial, radially” (see radial (adj.)); 3. “by means of radiant energy” (see radiate (v.)); 4. “radioactive” (see radioactive); 5. “by radio” (see radio (n.)).

pref.

1. Radiation; radiant energy:radiometer.
2. Radioactive:radiochemistry.
3. Radius:radiobicipital.