From The Collaborative International Dictionary of English v.0.48 :
Collude \Col*lude"\, v. i. [imp. & p. p. Colluded; p. pr. &
vb. n. Colluding.] [L. colludere, -lusum; col- + ludere to
play. See Ludicrous.]
To have secretly a joint part or share in an action; to play
into each other's hands; to conspire; to act in concert.
[1913 Webster]
If they let things take their course, they will be
represented as colluding with sedition. --Burke.
[1913 Webster]
From WordNet (r) 3.0 (2006) :
collude
v 1: 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" [syn: conspire,
collude]