◊ If you have an ace in the hole or an ace up your sleeve, you have a powerful and often secret weapon, advantage, etc., that you can use if it is needed.秘藏的王牌;秘密武器
The mayor's popularity among elderly voters gives him an ace in the hole for the coming election.市长深得老年选民的喜爱,这是他应对即将到来的选举的一张王牌。