have an ace up one’s sleeve

have an ace up (one's) sleeve

To have a secret plan, idea, or advantage that can be utilized if and when it is required. A reference to cheating at a card game by hiding a favorable card up one's sleeve. I have an ace up my sleeve for this race—my stamina. The other runners don't stand a chance! I hear that the defense attorney has an ace up her sleeve—a new eye-witness.
See also: ace, have, sleeve, up
Farlex Dictionary of Idioms.

have an ace up one’s sleeve

tv. to have something useful in reserve; to have a special trick available. (Have got can replace have.) I still have an ace up my sleeve that you don’t know about.
See also: ace, have, sleeve, up
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • a card up (one's) sleeve
  • ace up (one's) sleeve
  • have a card up (one's) sleeve
  • have a trick up (one's) sleeve
  • have an ace up (one's) sleeve
  • have an ace/a trick up your sleeve
  • have something up your sleeve
  • have up sleeve
  • have/keep something up your sleeve
  • trick up (one's) sleeve