Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
collūsĭo (conl-), ōnis, f. [colludo, II.], a secret, deceptive understanding, collusion, * Cic. Verr. 2, 3, 13, § 33: inter raptae patrem et raptorem, Sen. Contr. 2, 11, 22: per collusionem, id. ib. 5, 31 fin.: illa inter virum et uxorem nota collusio, App. Mag. p. 322, 13; Dig. 40, 16: de collusione detegendā, ib. 40, 4; 8, 5, 19; 17, 1, 8; 12, 2, 30, § 3.