Did you know…?
...that ‘ace up your sleeve’ started in 1500s. Back then people didn’t have pockets so they kept things hidden in their sleeves. Later on, magicians hid objects, even live small animals, up their sleeves and then pulled them out unexpectedly to surprise their audiences. In the 1800s dishonest card players secretly slipped a winning card, often an ace, up their sleeves and pulled it out to win the game.
Today it means a surprise or a secret advantage, especially something tricky that is kept hidden until needed.