Lewis & Short

collūsor (conl-), ōris, m. [colludo].

  1. I. A companion in play, playmate (in good prose), Cic. Phil. 2, 23, 56; 2, 39, 101; 5, 5, 13; * Suet. Calig. 41; Plin. Ep. 9, 33, 8; Dig. 11, 5, 1, § 1.
  2. * II. (Acc. to colludo, II.) He who has a secret understanding with one to the injury of a third, in law, Cod. Th. 7, 20, 2.