See: UP ONE'S SLEEVE.
{adv. phr.} 1. Hidden in the sleeve of one's shirt or coat and ready for secret or wrongful use. * /The crooked gambler hid aces up his sleeve during the card game so that he would win./ 2. {informal} Kept secretly ready for the right time or for a time when needed. * /Jimmy knew that his father had some trick up his sleeve because he was smiling to himself during the checker game./ Compare: CARD UP ONE'S SLEEVE. 3. See: LAUGH UP ONE'S SLEEVE.