Thick as thieves

Where does "thick as thieves" come from?

From the archives:

The Dictionary of Cliches by James Rogers (Ballantine Books, New York, 1985) says "thick as thieves" means "intimate, conspiratorially close." And it also refers to an 1833 quote -- from "The Parson's Daughter" by Theodore E. Hook. "She and my wife are thick as thieves, as the proverb goes."

This is based on a French saying "like thieves at a fair", which is an easily understood way of implying collusion. The adapted English form was indeed first used by the author Thomas Hook in "The Parson's Daughter" .