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