Merriam-Webster's Word of the Day for April 25, 2012 is:

cahoot • \kuh-HOOT\  • noun
: partnership, league — usually used in plural

Examples:
Police suspect that the burglar was in cahoots with the bartender.

"In a huge anti-mafia bust, 16 judges have been arrested near Naples, Italy, according to the BBC, for allegedly being in cahoots with Italy's notorious Camorra crime syndicate." — From a news article in The Huffington Post, March 19, 2012

Did you know?
"Cahoot" is used almost exclusively in the phrase "in cahoots," which means "in an alliance or partnership." In most contexts, it describes the conspiring activity of people up to no good. (There's also the rare idiom "go cahoots," meaning "to enter into a partnership," as in "they went cahoots on a new restaurant.") "Cahoot" may derive from French "cahute," meaning "cabin" or "hut," suggesting the notion of two or more people hidden away working together in secret. "Cahute" is believed to have been formed through the combination of two other words for cabins and huts, "cabane" and "hutte."