“In cahoots with” means in league with, or collaboration to nefarious ends. It’s also been used at times to mean a company or partnership.
The Oxford English Dictionary says that English got the expression from the Scots in the 1500s, with a little help from the French, more specifically, that the expression is “probably” from the French cahute, meaning a cabin or a poor hut.
Another theory is that word came to from French cohorte, or a slang form of English “cohort” in the meaning “accomplice.”
And yet another, from Jonathan Green’s Dictionary of Slang, which suggests that the word came from an American slang word “cahot” meaning pothole. That doesn’t ring true to me, but perhaps I just don’t like potholes.
The word (if it actually is the same one) reappeared as “cahoot” in early 1800s America, where the phrase “in cahoot” meant in partnership or in league with.
The OED‘s first citation comes from Chronicles of Pineville, a collection of sketches about backwoods Georgia by William T. Thompson from the early 1800s: “I wouldn’t swar he wasn’t in cahoot with the devil.”
The word “cahoot” apparently continued to be used in the singular for a couple of generations. The Oxford English Dictionary‘s first citation for the plural “cahoots” is from a manuscript diary of G. K. Wilder (1862): “Mc wished me to go in cahoots in a store.” And “cahoots” it’s been ever since.
Sometimes, being in a partnership is as claustrophobic as being confined to a small hut with no ventilation. But I like to imagine people “in cahoots” doing a little plotting and scheming towards things like practical jokes. And laughing while they do so.