The forgoing, for all its authority, is wisdom enough, but most folks don't (IMHO) care about the minute distinctions between the various definitions, though I do.
I gave up long ago, everywhere from choir practice to lessons to bands, trying to be very particular on this issue. I end up just calling any two or more notes sounding at the same time a chord, whether it's a "power chord" (love that rock guitar parlance otherwise known as a 5 chord) or an Em9 (which might be an Em2 if you want to confuse folks who only know chords by guitar shape rather than theory). More advanced students who have studied theory get this stuff quickly, and using particular definitions, but I think the casualness of music instruction in the rock/folk/pop disciplines encourages looser terminology usage. Fine, so long as everyone is "on the same page" and understands that theory gets pretty refined after some study.
A quick look through the (non-classical) beginner lesson books on my shelf, designed to get people playing rather than studying, confirms that a loose definition of musical terms is the order of the day. I wish these books came with a glossary or at least a disclaimer of some sort, but that might be asking too much.
Cool discussion, thanks friends. Mooh.