^ will listen to my next point.
Any decent argument is definition 2, definition 4 by it's own admission is obsolete, and definition 1 isn't a true debate in the style we consider when it happens inside the confines of your own mind; coloured as it is by your perceptions. Even if definition 1 happens outside your head, it could just be in argument form; or even a combative form. Definition 3 is the main one that I think we should consider.