up your sleeve

up (one's) sleeve

Of a plan or advantage, kept in secret so it 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. My stamina is the ace up my sleeve for this race—the other runners don't stand a chance! I've got a few tricks up my sleeve if he decides to pursue legal action against me.
See also: sleeve, up
Farlex Dictionary of Idioms.

up your sleeve

(of a strategy, idea, or resource) kept secret and in reserve for use when needed.
See also: sleeve, up
Farlex Partner Idioms Dictionary
See also:
  • up (one's) sleeve
  • up sleeve
  • a card up (one's) sleeve
  • ace up (one's) sleeve
  • have a card up your sleeve
  • have an ace up one’s sleeve
  • have an ace up your sleeve
  • have something up your sleeve
  • have up sleeve
  • trick up (one's) sleeve