Is 'co-conspirator' redundant?

Solution 1:

Usage of conspirator / co-conspirator has changed significantly over the past century or so...

But this applies only when it means others involved in the same conspiracy as an identified subject explicitly referenced. In all other contexts we still overwhelmingly use the "non-redundant" form...

Taking that distinction into account, I don't think co-conspirators is normally a "redundant" form. If I came across your conspirators today, I'd assume the person being addressed wasn't directly involved in the conspiracy at all. He might have been the one who stood to benefit from it, or who "bankrolled" them without knowing the details of the operation. Or perhaps he just suggested there might be a conspiracy...

"You're so cynical! Half the time I don't think your conspirators even exist!"

Solution 2:

I'm going to say that it isn't redundant. Two people can be conspirators, but in two different conspiracies. Co-conspirator tells us that they are conspiring together rather than conspiring with other people. So it provides us with an additional piece of information.

Solution 3:

Come to think of it, it might be superfluous in some cases.

However the word "co" might carry an important meeting in some other cases. The prefix "co", though it denotes equality in some usage (co-owner, co-teacher) might also suggest that one has a secondary or less important role (Think pilot, co-pilot). So we might use "co-conspirator" to call someone who had a minor role in a conspiracy, although it's true that we also use this term to describe people who had equal participation in the conspiracy. In this instance, it does appear to be redundant--but something that's considered reputable usage.

So I wouldn't say that "co" in "co-conspirator" is entirely useless.