heater

noun

1. an apparatus for heating or warming a room, car, water, etc.; stove, furnace, radiator, etc.
2. a person whose work is to heat something
3. in an electron tube, an element set inside the cathode and heated by an electric current so that it indirectly heats the cathode to the temperature at which it will give off electrons
4. ☆ Slang a pistol
5. Baseball, Slang a fastball