I was a little concerned about whether to offer the word cahoots on its own or the phrase in cahoots because that’s typically how it’s used. You would hear something like, “I think Bob and Tom are in cahoots” but rarely, I suspect “Bob and Tom are cahoots.” The other variation is to add the word with to create the phrase in cahoots with.
Its American origin is noted by the OED with their first reference coming from John Russell Bartlett’s 1848 Dictionary of Americanisms. “Pete Hopkins ain’t no better than he should be, and I wouldn’t swar he wasn’t in cahoot with the devil.” (Chronicles of Pineville, p. 74).
What’s interesting is that Oxford say that it “probably” derives from the French cahute, which means a cabin or a poor hut, but Bartlett suggests it is a corruption of the word cohort, which exists in both French and Spanish. I’m swayed by the latter considering that the word was also apparently first noted in the South and West of the US – both areas influenced by the French and Spanish languages.
Cohort /’kəʊhɔ:t/ originally referred to a company of soldiers, more specifically a tenth of a legion. By the 1500s it was used for a band of warriors in general and in the 1700s took on the meaning of a company of persons in defence of a common cause. This certainly fits with the notion of being in cahoots.
And thanks to Lisa Fannin for the suggestion.