Where does the phrase “let the cat out of the bag” come from and What does it mean?

If all the truth were known, our ancestors probably knew and practiced more sales tricks than the sliest and most unscrupulous merchants ever heard of today.

Elsewhere is told one reason why a n was warned not “to buy a pig in poke,” but, so it is said, was another more potent reason, one might not get even a stunted piglet; the wriggling contents of the bag, so like a lively pig, might be a cat.

A luckless tradesman, who may not have examined each poke carefully that he had bought from a countryman, indeed “let the cat out of the bag” when the housewife insisted upon seeing the quality of the pig she thought of buying.

Once a literal statement, we use the expression nowadays with the meaning, to disclose something that has been kept secret.

Literary use of the saying is not very old, going back only about two hundred years, but in common speech it is likely that usage antedates that by another two hundred years at least.