To be in cahoots with someone means to be secretly working together, usually for a sneaky or dishonest purpose. When two students are in cahoots, they might be plotting to skip homework or planning a surprise party. The phrase always suggests partnership and secrecy.

You'll usually hear this as “in cahoots with” someone. If your teacher catches two friends passing notes during a test, she might suspect they're in cahoots to cheat. When a detective discovers that the butler and the gardener were in cahoots to steal the jewelry, it means they planned and carried out the theft together.

The word cahoots itself is rarely used alone. You can't have “a cahoot” or be “cahooting around.” It almost always appears in this phrase, which makes it a bit unusual in English.

While being in cahoots often implies something mischievous or wrong, it can also describe harmless secret cooperation. Two siblings might be in cahoots to surprise their parents with breakfast in bed, or friends might be in cahoots to plan a birthday surprise. The word always carries that sense of conspiracy and secrecy, whether the plan is innocent fun or actually troublesome.