'Heater' definitions:

Definition of 'heater'

From: WordNet
noun
Device that heats water or supplies warmth to a room [syn: heater, warmer]
noun
(baseball) a pitch thrown with maximum velocity; "he swung late on the fastball"; "he showed batters nothing but smoke" [syn: fastball, heater, smoke, hummer, bullet]

Definition of 'Heater'

From: GCIDE
  • Heater \Heat"er\ (h[=e]t"[~e]r), 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]
  • Feed heater. See under Feed. [1913 Webster]

Synonyms of 'heater'

From: Moby Thesaurus