Source : Webster's Revised Unabridged Dictionary (1913)

Radio \Ra"di*o\, a.
   Of or pertaining to, or employing, or operated by, radiant
   energy, specifically that of electric waves; hence,
   pertaining to, or employed in, radiotelegraphy.

Source : WordNet®

radio
     adj : indicating radiation or radioactivity; "radiochemistry"

radio
     n 1: medium for communication [syn: {radiocommunication}, {wireless}]
     2: an electronic receiver that detects and demodulates and
        amplifies transmitted signals [syn: {radio receiver}, {receiving
        set}, {radio set}, {tuner}, {wireless}]
     3: a communication system based on broadcasting electromagnetic
        waves [syn: {wireless}]

radio
     v : transmit messages via radio waves; "he radioed for help"