collusion (n.)

"secret agreement for fraudulent or harmful purposes," late 14c., from Old French collusion and directly from Latin collusionem (nominative collusio) "act of colluding," from colludere, from assimilated form of com "with, together" (see com-) + ludere "to play" (see ludicrous). "The notion of fraud or underhandedness is essential to collusion" [Fowler].