n. 1. One who, or that which, heats. [ 1913 Webster ]
2. Any contrivance or implement, as a furnace, stove, or other heated body or vessel, etc., used to impart heat to something, or to contain something to be heated. [ 1913 Webster ]
3. A pistol or other carryable firearm; as, gunmen with their heaters bulging in their pockets. [ slang ] [ PJC ]