The story
From the practice of magicians hiding tricks or gimmicks in the sleeve.
Etymology from Wiktionary, CC BY-SA 4.0.
up one's sleeve
Today it means: Hidden and ready to be produced as needed; in reserve. Full definition →
Today it means: Hidden and ready to be produced as needed; in reserve. Full definition →
From the practice of magicians hiding tricks or gimmicks in the sleeve.
Etymology from Wiktionary, CC BY-SA 4.0.