ace in the hole

A major advantage that one keeps hidden until an ideal time. The phrase originated in poker, in which an ace is the most valuable card. Primarily heard in US. His embarrassing secret is my ace in the hole, and I plan to reveal it to everyone the next time he mocks me publicly.

Fig. something important held in reserve. The twenty-dollar bill I keep in my shoe is my ace in the hole.

A hidden advantage or resource kept in reserve until needed, as in The prosecutor had an ace in the hole: an eyewitness. The term comes from stud poker, where each player is dealt one card face down-the so-called hole card-and the rest face up. Should the hole card be an ace, the player has a hidden advantage. Hole here simply means "a hiding place." In the 19th-century American West, the expression was used to refer to a hidden weapon, such as a gun concealed in a shoulder holster. By the 1920s it had become a metaphor for any surprise advantage or leverage.

A hidden advantage or resource kept in reserve until needed.