Let The Cat out of The Bag
Meaning
To reveal a secret.
Example
Don’t let the cat out of the bag about Karla’s birthday present.
Origin
At medieval markets, unscrupulous traders would display a pig for sale. However, the pig was always given to the customer in a bag, with strict instructions not to open the bag until they were someway away. The trader would hand the customer a bag containing something that wriggled, and it was only later that the buyer would find he’d been conned when he opened the bag to reveal that it contained a cat, not a pig. Therefore, letting the cat out of the bag revealed the secret of the con trick.
At one time and even today in some circles, some people who have unwanted cats put them in a gunny sack with some large rocks and drop the whole thing in the river. Some people would find this practice objectionable – hence a desire to keep it a secret. Letting the cat out of the bag would divulge that secret.
