cahoots

cahoots \kuh-HOOT\, noun:

In partnership; in league.

The soldier could only have concluded that my grandfather was in serious cahoots with John Brown, and attention of that kind could destroy everything.
-- Marilynne Robinson, Gilead: A Novel

The dreamers did not know that Kuyo and I, as if in cahoots with the soldiers, had trapped and imprisoned them on the island.
-- Russell Banks, The Darling: A Novel

Cahoots enters English in the United States in the 1800s, possibly derived from the French cahute, "cabin, hut," but others trace it to the roots of the English word cohort.