✔ let the cat out of the bag
If you let the cat out of the bag, you let someone know a secret.
■ For example:
- We’d planned a surprise party for Donna, but some guy she works with let the cat out of the bag, so now she knows.
- Don’t forget that this is a secret, so whatever you do, don’t let the cat out of the bag.
Origin: Possibly related to the fact that in England in the Middle Ages, piglets were usually sold in bags at markets. Sometimes, someone would try to cheat a buyer by putting a cat in one of the bags instead of a piglet. And if someone let the cat out of the bag, the fraudster’s secret was revealed.