trump card: Meaning and Definition of

trump card

Pronunciation: (trump' kärd" for 1 trump' kärd' for 2). [key]
  1. trump (def. 1a).
  2. something that gives one person or group the advantage over another: The surprise witness was his trump card.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.