col·lude 
(kə-ld)
(kə-ld)intr.v. col·lud·ed, col·lud·ing, col·ludes
To act together, often in secret, to achieve an illegal or improper purpose: "The managers and the union leaders regularly colluded to rob the plantations at the expense of the workers" (Daniel Wilkinson).
[Latin collūdere : com-, com- + lūdere, to play; see leid- in the Appendix of Indo-European roots.]
col·luder n.