Source : Webster's Revised Unabridged Dictionary (1913)

Heater \Heat"er\, n.
   1. One who, or that which, heats.

   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.

   {Feed heater}. See under {Feed}.

Source : WordNet®

heater
     n 1: device that heats water or supplies warmth to a room [syn: {warmer}]
     2: (baseball) a pitch thrown with maximum velocity; "he swung
        late on the fastball"; "he showed batters nothing but
        smoke" [syn: {fastball}, {smoke}, {hummer}, {bullet}]