trump card

trump-card的词性：
n.（名词）

1. Games A card in the trump suit, held in reserve for winning a trick.
【游戏】 王牌：一盒王牌中的一张，留在手里以备赢一圈牌

2. A key resource to be used at the opportune moment; a trump:
王牌：适当时刻所运用的关键手段；王牌：

“[They] seem determined to use the agreement as a trump card to obtain . . . all the advantages they feel they deserve” (Christian Science Monitor)
“［他们］ 似乎决定要把协议改作为一张王牌以取得…他们认为应得的所有优势” (基督教科学箴言报)