WordNet records no synonym and no antonym for radiator. It is the only member of each of its synsets, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
any object that radiates energy
heater consisting of a series of pipes for circulating steam or hot water to heat rooms or buildings
Synonyms, antonyms and the broader and narrower relations for radiator come from Princeton University’s WordNet. Full sources and licences.
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