have up sleeve

have (something) 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 a few tricks up my sleeve if he decides to pursue legal action against me. She has all the details of their unscrupulous business practices up her sleeve if they ever try to fire her.
See also: have, sleeve, up
Farlex Dictionary of Idioms.

have something up one's sleeve

 and have an ace up one's sleeve
Fig. to have a secret or surprise plan or solution (to a problem). (Alludes to cheating at cards by having a card hidden in one's sleeve.) I've got something up my sleeve, and it should solve all your problems. I'll tell you what it is after I'm elected. The manager has an ace up her sleeve. She'll surprise us with it later.
See also: have, sleeve, up
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • a card up (one's) sleeve
  • ace up (one's) sleeve
  • card up one's sleeve
  • have a card up your sleeve
  • have an ace up (one's) sleeve
  • have an ace up one’s sleeve
  • have an ace up your sleeve
  • have an ace/a trick up your sleeve
  • have/keep something up your sleeve
  • trick up (one's) sleeve