Pronunciation: (ku-lOO'zhun),[key] —n. 1. a secret agreement, esp. for fraudulent or treacherous purposes; conspiracy: Some of his employees were acting in collusion to rob him. 2. Law.a secret understanding between two or more persons to gain something illegally, to defraud another of his or her rights, or to appear as adversaries though in agreement: collusion of husband and wife to obtain a divorce.