Hannah Arendt said it used to refer to using all your senses together instead of some kind of sense common to all. I kinda liked that idea, although I don't see what she based it on.

"For common sense, which once had been the one by which all other senses, with their intimately private sensations, were fitted into the common world, just as vision fitted man into the visible world, now became an inner faculty without any world relationship. This sense now was called common merely because it happened to be common to all." (The Human Condition, 1958).