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.

A hidden advantage. In stud poker the dealer gives each player a card facedown, called a “hole card”; from that point on all other cards are dealt faceup. Should the hole card be an ace, a high card, the player has an advantage unknown to his opponents. Stud poker was first introduced shortly after the Civil War and played mostly in what is now the Midwest but then was the West. In time “ace in the hole” became western slang for a hidden weapon, such as a gun carried in a shoulder holster, and by the early 1920s it was used figuratively for any hidden leverage. The related ace up one’s sleeve comes from the practice of dishonest gamblers who would hide a winning card in just this way. See also up one's sleeve.