To let the cat out of the bag means to reveal a secret or surprise by accident.
Tell people a secret, without intention.
Give away a secret.
1. Heather is expecting a baby but wants to surprise the family. Let’s not let the cat out of the bag.
2. She let the cat out of the bag when she blurted out the secret yesterday.
3. Grandma let the cat out of the bag during the family reunion and everyone got emotional.
4. You’d better not let the cat out of the bag with our pregnancy news. I want to surprise everyone during the family photo!
betray, blab, blow, disclose, divulge,leak, let slip, mouth, sing, spill, spill the beans, squawk, squeal, tattle, tell, tell a secret