D defs.my
Entry 3 senses Webster, 1913

Heater

/(hēt"ẽr)/ · Heat·er · IPA /ˈhitɚ/
01 n. One who, or that which, heats.
  1. 1.
    One who, or that which, heats.
  2. 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.
  3. 3.
    A pistol or other carryable firearm; as, gunmen with their heaters bulging in their pockets.[slang]
Phrases & compounds
Feed heater — See under Feed.