trump-card
n
(a) card of the suit that is trumps 王牌; 将牌; 主牌.
(b) (fig 比喻) way of gaining what one wants, esp after trying other ways; most valuable resource 为达到目的采取的方法(尤指已试过其他方法); 最有效的一招
Finally she played her trump-card and threatened to resign. 最後她使出了绝招, 扬言要辞职.