keep (something) up (one's) sleeve(redirected from keep up their sleeve)
keep (something) up (one's) sleeve
To keep something, such as a plan or advantage, 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. What the other runners don't know is that I've kept an ace up my sleeve for this race—my stamina. I've been keeping a few tricks up my sleeve if he decides to pursue legal action against me.