Green’s Dictionary of Slang

(US) to act in partnership.

1857		N.Y. Herald 20 May (B). n.p.: They all agree to cahoot with their claims against Nicaragua and Costa Rica [DA].
1868		Tarboro’ Southerner (NC) 28 May 4/2: He was fond of paddling his own canoe, and seldom cahooted with any one.
1872		Schele De Vere Americanisms 106: The old English word cahoot, a slang word of the West and South for keeping company legitimately and illegitimately, is so little used and so far removed from its original in French (cohorte) that it does not deserve a place among Americanisms.
1886		S.W. Mitchell Roland Blake 261: The women ken cohoot together down at the old house.
1948		Chicago Trib. 1 Aug. [comic strip] 6: Why don’t cha feud fa’r an’ squar’ — with shootin’ arns instead o’ gossip thet he’s cahooting with speerits? [DA].