trump card definition by American Heritage Dictionary
- Games A card in the trump suit, held in reserve for winning a trick.
- A key resource to be used at an opportune moment; a trump: “[They] seem determined to use the agreement as a trump card to obtain … all the advantages they feel they deserve” (Christian Science Monitor).
trump card - Cultural Definition
In general, something capable of making a decisive difference when used at the right moment; in certain card games, trump is the suit designated as having precedence over the others: “The prosecutor was about to win the case, when the defense lawyer produced her trump card: an eyewitness who testified that the accused was nowhere near the scene of the crime.”