1) Act in unison 2) Cabal 3) Conspire 4) Interact 5) To conspire in a fraud 1) Plot 
• (v. i.) To have secretly a joint part or share in an action; to play into each other`s hands; to conspire; to act in concert.
Col·lude' intransitive verb [ imperfect & past participle Colluded ; present participle & verbal noun Colluding .] [ Latin colludere , - lusum ; col- + ludere to play. See Ludicrous .] To have secret...
collude 1. To act together secretly to achieve a fraudulent or deceitful purpose; to connive. 2. To act in secret concert with, chiefly in order to trick or baffle some third person or party. 3. To play into one another's hands; to conspire, to plot, to connive; and to play falsely. 4. To act in unison, or agreement, and in secret towards a decei...
verb 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 act together through a secret understanding, esp. with evil or harmful intent. · to conspire in a fraud.