Source : Webster's Revised Unabridged Dictionary (1913)

Tipster \Tip"ster\, n. [Tip a hint + -ster.]
   One who makes a practice of giving or selling tips, or
   private hints or information, esp. for use in gambling upon
   the probable outcome of events, as horse races.

Source : WordNet®

tipster
     n : one who sells advice about gambling or speculation
         (especially at the racetrack) [syn: {tout}]