You almost always meet this word in one phrase: in cahoots (with someone). It means two people, or two groups, are secretly working together, usually toward something a bit dishonest or sneaky — not an open, honest team. It is informal, a little old-fashioned and folksy, and it has a grin of blame in it. You would not put it in a contract. You also do not really say a cahoot; the -s is stuck to the word, the way trousers keeps its -s. There is a rare older verb, to cahoot, “to join in a secret plan,” but ordinary talk almost never uses it. People reach for the phrase instead. Though actually, not every shared plan is cahoots. Teachers planning a party are not in cahoots. Two shops quietly raising prices together are.