have/keep something up your 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 a card up her sleeve if they ever try to fire her, since she knows about the boss's unscrupulous business practices.
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.
have something up your sleeve
COMMON If you have something up your sleeve, you have a secret idea or plan which you can use to gain an advantage over other people. Paterson had another plan up his sleeve, however. If that failed, he had one final trick up his sleeve. We would wait to see what Bill had up his sleeve. Note: You can also just talk about something, such as a plan or a trick, that is up someone's sleeve. The manager insisted his team will use every trick up their sleeve to defeat their rivals. Note: The expressions have an ace up your sleeve and have a card up your sleeve mean the same. He always seems to have an ace up his sleeve to deal with these kinds of situations. Even his critics admit that he seems always to have a card up his sleeve. Note: If someone wanted to cheat at cards, they could hide a good card up their sleeve to use at an appropriate time.