To be working together in secret, often with an air of unseemliness. Those two have been whispering all day. I wonder what they're in cahoots about.I think all of those kids are in cahoots because they're all on the surveillance video from the night of the robbery.
to be secretly planning something together, especially something dishonest (usually + with ) There are theories that someone in the government was in cahoots with the assassin.