NOUN (3)

1. any object that radiates energy;

2. heater consisting of a series of pipes for circulating steam or hot water to heat rooms or buildings;

3. a mechanism consisting of a metal honeycomb through which hot fluids circulate; heat is transferred from the fluid through the honeycomb to the airstream that is created either by the motion of the vehicle or by a fan;

The Collaborative International Dictionary of English v.0.48:

Radiator \Ra"di*a`tor\ (r[=a]"d[i^]*[=a]`t[~e]r), n.
   1. 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.
      [1913 Webster]

   2. Any of various devices for cooling an internal substance
      by radiation, as a system of 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.
      [Webster 1913 Suppl.]

   3. (Wireless Teleg.) An oscillator.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

radiator
    n 1: any object that radiates energy
    2: heater consisting of a series of pipes for circulating steam
       or hot water to heat rooms or buildings
    3: a mechanism consisting of a metal honeycomb through which hot
       fluids circulate; heat is transferred from the fluid through
       the honeycomb to the airstream that is created either by the
       motion of the vehicle or by a fan

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "radiator":
   AM transmitter, Bunsen burner, Dutch oven, FM transmitter,
   RT transmitter, alpha radiator, amateur transmitter, beacon,
   bedpan, beta radiator, bloom heater, brazier, brick oven,
   calefactory, car heater, defroster, dielectric heater,
   dielectric preheater, electric blanket, electric heater,
   electronic heater, fan marker, fireless heater, fission products,
   fluorescent paint, foot warmer, forge, gamma radiator, gas log,
   geyser, heat lamp, high-frequency heater, hot-water bag,
   hot-water bottle, hot-water heater, induction heater,
   infrared heater, infrared lamp, ingot heater, iron heater,
   kerosene heater, kiln, microphone, orchard heater, oven, preheater,
   radio beacon, radio range beacon, radio transmitter,
   radio-frequency heater, radioactive waste, radiocarbon,
   radiocopper, radioelement, radioiodine, radioisotope,
   radiomicrophone, radiosonde, radiothorium, radium dial,
   radium paint, register, sun lamp, tracer, tracer atom,
   tracer element, transceiver, transmitter