Let the Cat Out of the Bag

Meaning

When someone lets the cat out of the bag, they reveal information that was supposed to stay secret. The reveal is often accidental — a slip of the tongue, a careless comment, or telling the wrong person at the wrong time. The phrase carries the idea that once the secret is out, you cannot take it back.

This idiom is very common in everyday English. It is frequently used about surprises, plans, news, or private information. People say things like “Don’t let the cat out of the bag” as a warning to keep quiet, or “Who let the cat out of the bag?” when a secret has been spoiled.

It usually has a light, slightly playful tone, though it can also describe more serious leaks of information. The key idea is that a hidden thing has suddenly become known.

Origin

The most popular explanation links the idiom to medieval market fraud. Dishonest sellers would sometimes promise a buyer a young piglet, place it in a sack, and then secretly substitute a cat. If the buyer opened the bag before getting home, the trick was exposed — the cat would jump out, and the fraud was revealed. Letting the cat out of the bag therefore meant exposing a hidden truth.

The same market story is often connected to the idiom “to buy a pig in a poke,” where a “poke” is an old word for a bag. Buying a pig in a poke meant paying for something sight unseen — and discovering a cat instead. Idioms like this are the kind of expression documented in general reference works such as the Cambridge Dictionary, which record how figurative meanings develop in everyday English.

The figurative phrase has appeared in English writing since at least the 18th century, and it remains one of the most widely used idioms in the language today.

Example Sentences

Dialogue Example

Usage Notes

This idiom is informal and very common in both British and American English. The verb “let” stays the same in the present and past tense, with “letting” and “lets” as the other forms. You can add an adverb, as in “accidentally let the cat out of the bag.” It is often used in warnings with “don’t.”

Common Mistakes

Learners sometimes change the wording to “let the cat out of the box” or “open the bag.” The fixed phrase is let the cat out of the bag. Also, remember it means to reveal a secret, not to release an animal — do not use it literally about a real cat.

Related Idioms

Want to understand the grammar behind this? Explore our Grammar guides.

Quick Check: Let the Cat Out of the Bag

2 questions — test what you just learned.

1. What does “Let the Cat Out of the Bag” mean?

Describes a comment, story, or experience that affects someone personally and uncomfortably, because it…To reveal a secret, often accidentally or carelessly.To make an error or fail to do something important, often letting other people down.

2. Complete the sentence: “We wanted to surprise Grandma, but my little brother _____ at dinner.”

let the cat out of the bagDrop the ballClose to home

Want more practice? Try the full Quiz exercise →

Frequently Asked Questions

What does "let the cat out of the bag" mean?

It means to reveal a secret, often accidentally or before the right time. Once the secret is out, it cannot be taken back.

How do you use "let the cat out of the bag" in a sentence?

You can say "Don’t let the cat out of the bag" as a warning, or "He let the cat out of the bag about the surprise party." It usually describes revealing a secret.

Where does "let the cat out of the bag" come from?

The popular explanation comes from medieval market fraud. Sellers sometimes hid a cat in a bag in place of a piglet. Opening the bag exposed the cat — and the trick — so revealing a secret became "letting the cat out of the bag."

Is "let the cat out of the bag" formal or informal?

It is informal but very widely used. You can hear it in casual conversation, on the news, and in workplaces, though it is not suited to very formal writing.

What is a similar idiom to "let the cat out of the bag"?

A very close idiom is "spill the beans," which also means to reveal a secret. "Give the game away" is another similar expression.

Is the secret usually revealed on purpose?

Often it is accidental — a slip of the tongue or a careless comment. However, it can also describe revealing a secret deliberately at the wrong moment.

Can you say "the cat is out of the bag"?

Yes. "The cat is out of the bag" means the secret is already known. It focuses on the result, while "let the cat out of the bag" focuses on the action of revealing it.

Is this idiom used in American English?

Yes. It is common in both British and American English and is understood by speakers everywhere.

What are common ways to use this idiom?

Common forms include "Don’t let the cat out of the bag," "Who let the cat out of the bag?" and "She accidentally let the cat out of the bag."

What English level is "let the cat out of the bag" suitable for?

It is suitable for A2 (Elementary) learners. The vocabulary is simple and the idiom is very common, making it a good early idiom to learn.