Ace in the Hole is a slang expression meaning a secret or extra asset to assure success, referring to the ace playing card a player has as a hole card (or face down card) in a game of stud poker.

References to this expression include:

• "Ace in the Hole", a 1909 Tin Pan Alley popular song by James Depsey and George Mitchell
• Ace in the Hole (1951 film), a film made in 1951 starring Kirk Douglas
• "Ace in the Hole", a 1979 song by Paul Simon.
• "Ace in the Hole", a song by George Strait
• "Ace in the Hole", a duet by Johnny Mercer & Bobby Darin
• "Ace in the Hole", song by Connie Francis
• "Ace in the Hole", song by Bunk Johnson & Lu Watters
• "Ace in the Hole", song by Dave Van Ronk
• "Ace in the Hole", song by Jan Menzies
• "Ace in the Hole", song by Bob Scobey
• "Ace in the Hole", song by Dukes of Dixieland
• Ace in the Hole (book), a science fiction book in the Wild Cards series
• "You are my 'ace in the hole,' as we say in America. I have a stone in my shoe. You can remove it." Don Altobello said, "Only one stone?" Mosca asked - God Father III

English idioms | Slang expressions