ace in the hole
一个秘密的策略、计划或资源，可以在紧急情况下使用
口语·书面语·形容秘密优势或杀手锏
英文释义
a secret advantage or resource that can be used in a situation when it is needed
例句
The team kept their star player as an ace in the hole for the final match.
典故来源
源自扑克游戏，玩家暗藏一张王牌（ace）在手中，关键时刻打出制胜。