from Wiktionary, Creative Commons Attribution/Share-Alike License
- To disclose a secret; to let a secret be known, often inadvertently.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- v. divulge confidential information or secrets
(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. (Wiktionary)
Whoever he is — say ‘he’ for argument’s sake — he thinks the Captain’s let the cat out of the bag about you coming up here and that you’d be off guard and wide-open to another welt on the napper?