let the cat out of the bag

Definition

To disclose a secret; to let a secret be known, often inadvertently.

Etymology

(Mid-1700s) The inverse of the idiom pig in a poke. If a dishonest merchant tries to sell a cat as a pig and the cat comes out or is taken out of the bag, the merchant's secret is disclosed.

Example Sentences

• "It was going to be a surprise party until someone let the cat out of the bag."
• "[H]e proved himself as decent, decorous, and conscientious, as Peter was rampant, boisterous, and —— (this last epithet I choose to suppress, because it would let the cat out of the bag)."