(1):
(n.) That which radiates or emits rays, whether of light or heat; especially, that part of a heating apparatus from which the heat is radiated or diffused; as, a steam radiator.
(2):
(n.) Any of various devices for cooling an internal substance by radiation, as a system og rings on a gun barrel for cooling it, or a nest of tubes with large radiating surface for cooling circulating water, as in an automobile.
(3):
(n.) An oscillator.