have a card up your sleeve
暗中保留一张杀手锏，以便在关键时刻使用
口语·表示有备用策略
英文释义
to have a secret plan or advantage that can be used if needed
例句
Don't worry, I have a card up my sleeve if the negotiation goes wrong.
典故来源
源自魔术或赌博中藏牌作弊的手法，比喻暗中保留优势或计划。