n (uncountable) The technology that allows for the transmission of sound or other signals by modulation of electromagnetic waves.
n (countable) A device that can capture (receive) the signal sent over radio waves and render the modulated signal as sound.
n (Internet|uncountable) The continuous broadcasting of sound recordings via the Internet in the style of traditional radio.
v (intransitive|transitive|ambitransitive) To use two-way radio to transmit (a message) (to another radio or other radio operator).