Once a term gets carved in the stone of shop manuals and parts catalogs, that’s what the thing is forever, regardless of how poor the fit is between the part and the function and the word. A “constant-velocity” joint is just such a mismatch: the joint doesn’t turn at a constant velocity; it moves a roughly the speed the driveshaft does, as the motorist decides. What’s more, as we’ll see, different parts of the joint rotate at speeds varying from the driveshaft, and for a very good reason.