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.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
have something up one's sleeveand 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.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.