A SHADY character is skulking around the language of our media: the co-conspirator. If a conspirator is someone who conspires, what is a co-conspirator? It couldn't be an individual who co-conspires, because there is no such verb. Black's Law Dictionary speaks of conspirators as "two or more persons" entering on a criminal offense. (My Random House and American Heritage dictionaries do not even list co-conspirator.)
Perhaps the "co" is to hint at a status of an adjunct conspirator, someone marginally connected with the plot. But that would still make him a "conspirator on the fringes of it."
To conspire literally means to "breathe together." It conjures up an image of plotters in a tight huddle, their breaths blending. "Conspirator" thus implies accomplices, or at least one other comrade in crime. If "lone conspirator" is a contradiction in terms, doesn't "co-conspirator" belong to the likes of "free gift," "advance warning," and "redundant tautology"? An example of this would be "fellow co-conspirator." Maybe we'd better stop before this conspiratorial inquiry gets out of hand.