Lewis & Short

collūdĭum (conl-), ii, n. [colludo] (post-class.).

  1. I. A sporting, playing together: delphinorum, Sol. 12; so Symm. Ep. 3, 5.
  2. II. A secret, deceptive understanding, collusion, esp. in justice, Amm. 18, 5, 1; Cod. Th. 9, 42, 20; 11, 42, 7; Symm. Ep. 4, 20.