Let the Cat Out of the Bag
To let the cat out of the bag is to reveal a secret, often unintentionally. Phrase Finder and Word Histories both document a 1760 London Magazine use. Popular market-swindle and cat-o’-nine-tails explanations are kept separate from that secure chronology because the reviewed evidence does not directly establish either as the phrase’s origin.
It means to reveal secret information, especially by accident or before it was meant to be disclosed.
Key details
What the evidence supports
The expression is documented in print in 1760 with the disclosure sense.
Phrase Finder and Word Histories both report the London Magazine example from 1760.
The idiom comes from a market fraud in which a cat was substituted for a pig in a sack.
Phrase Finder considers this more plausible than the naval story but says it found no direct documentary evidence linking the practice to the idiom.
The “cat” is the naval cat o’ nine tails removed from a bag before punishment.
Phrase Finder calls the nautical explanation dubious and notes that it does not naturally account for the “disclose a secret” meaning.
Documented timeline
- 1760
London Magazine use reported
Two reviewed specialist sources report a 1760 London Magazine example already using the expression in a disclosure context.
- 1761
Another printed use reported
Word Histories reports Thomas Mortimer using the expression in Every Man his Own Broker (1761).
Unresolved evidence
Which popular origin story, if any, explains the idiom?
The reviewed sources support the 1760 documentary chronology but do not establish either the market-swindle or naval punishment story as the origin.
Variants
Current Cambridge form.
Meaning over time
Secret-disclosure sense
Reveal information that was meant to remain secret, often unintentionally.
Further guidance
Meaning
Cambridge defines the idiom as allowing a secret to become known, usually without intending to.
Origin boundary
The pig-in-a-poke story has contextual plausibility but no direct documentary link in the reviewed source; the naval cat-o’-nine-tails story is treated as weaker.
Secure Chronology
Both reviewed history sources point to a 1760 London Magazine use with the modern disclosure sense.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- LET THE CAT OUT OF THE BAG definition (opens in a new tab)Cambridge Dictionary · Current idiomatic meaning
- Let the cat out of the bag — meaning and origin (opens in a new tab)Phrase Finder · 1760 chronology and review of competing origin stories
- The authentic origin of “to let the cat out of the bag” (opens in a new tab)Word Histories · Independent review of 1760 and 1761 printed evidence