Radio- : A combining form indicating connection with, or relation to, a radius or ray; specifically (Anat.), with the radius of the forearm; as, radio-ulnar, radio-muscular, radio-carpal.

Example:
What causes the radio in a clock radio to come on by itself?

Taxonomy
radio, signals, frequency, receiver, radio signals, radio waves, radio frequency, broadcast, aircraft, radars, radio receiver, satellites, amplitude, transmitters, military, wireless, energy, QAM.

Defination from the web:
radio including invention, history, and the use of radio waves for video, telephony, navigation, and radar.