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).
(intransitive) to act in concert with; to conspire
act in unison or agreement and in secret towards a deceitful or illegal purpose;
The two companies conspired to cause the value of the stock to fall
To have secretly a joint part or share in an action; to play into each other's hands; to conspire; to act in concert.
If they let things take their course, they will be represented as colluding with sedition.