The Collaborative International Dictionary of English v.0.48:

Collusive \Col*lu"sive\, a.
   1. Characterized by collusion; done or planned in collusion.
      "Collusive and sophistical arguings." --J. Trapp.
      "Collusive divorces." --Strype.
      [1913 Webster]

   2. Acting in collusion. "Collusive parties." --Burke. --
      Col*lu"sive*ly, adv. -- Col*lu"sive*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

collusive
    adj 1: acting together in secret toward a fraudulent or illegal
           end [syn: collusive, conniving]