a/your trump card
1. A designated card in some card games that ranks above all others. The only way I can win this hand is if I get the trump card.
2. A resource used to gain an advantage over others, often by being held and then used at an opportune time. I have a feeling the prosecution still hasn't played their trump card in this trial—I expect a big revelation during tomorrow's testimony.
A key resource to gain an advantage at the opportune moment, as in That surprise witness was the defense's trump card, or She played her trump card, announcing that the Senator would speak. This expression transfers the trump card of games such as bridge, which can win over a card of another suit, to other kinds of advantage. [Early 1800s]
a/your ˈtrump cardsomething that gives you an advantage over other people, especially when they do not know what it is and you are able to use it to surprise them: Many schools use small classes as their trump card in marketing campaigns. ♢ He waited until the last minute to play his trump card and tell them about his plans to cut costs.
In some card games, one of the four suits is chosen to have a higher value than the others. The cards in that suit are trump cards.