Webster's Revised Unabridged Dictionary · 1913

Of or pertaining to, or employing, or operated by, radiant energy, specifically that of electromagnetic waves with frequencies between those of infrared radiation and X-rays; hence, pertaining to, or employed in, broadcast radio or television, microwaves, radiotelephones, etc.; as, radio waves.

of or pertaining to broadcast radio; as, a radio program.

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