secret or illegal cooperation or conspiracy, especially in order to cheat or deceive others
This isn’t a very nice word. I wonder, though, if a second meaning is beginning to emerge through common usage—one not involving illegality or cheating or deceit. The definition above, from the Oxford American Dictionary, already hints at this with the word especially. Note the difference between that definition and the one from The American Heritage Dictionary: “A secret agreement between two or more parties for a fraudulent, illegal, or deceitful purpose.” The Merriam-Webster Dictionary‘s definition, which also uses especially, seems to leave the most room for a more neutral connotation: “secret agreement or cooperation especially for an illegal or deceitful purpose.” My guess is that as the word continues to be used outside of the legal profession, its meaning will become more generalized to the point where people will, given the proper context, understand it to mean “a secret agreement or activity between two or more parties.” But, that’s only a guess. Who knows? Maybe that has already happened.