Source : Webster's Revised Unabridged Dictionary (1913)

Betrayer \Be*tray"er\, n.
   One who, or that which, betrays.

Source : WordNet®

betrayer
     n 1: one who reveals confidential information in return for money
          [syn: {informer}, {rat}, {squealer}, {blabber}]
     2: a person who says one thing and does another [syn: {double-crosser},
         {double-dealer}, {two-timer}, {traitor}]