trump card(redirected from play one's 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]