Source : Webster's Revised Unabridged Dictionary (1913)

Warner \Warn"er\, n.
   One who warns; an admonisher.

Warner \Warn"er\, n.
   A warrener. [Obs.] --Piers Plowman.

Source : WordNet®

Warner
     n 1: United States filmmaker who with his brothers founded the
          movie studio that produced the first talking picture
          (1881-1958) [syn: {Charles Dudley Warner}]
     2: someone who gives a warning to others