ace in the hole

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.