It used to also mean "well equipped" or "well provided for" which when read in context to the Second Amendment makes the whole thing a lot clearer.
It's the militia that needs to be "well-regulated" not the guns, although that would obviously be a Good Thing too. In this context "Well regulated" meant and means today, properly functioning, fit for it's intended purpose. One purpose of the militia was said to be to prevent the establishment of a standing army, or if such an army were to be raised, to be able to overwhelm it if it were turned to tyrannical ends, rather than defending the nation from foreign threats. The other purpose of course was to defend the country, from both foreign and domestic enemies. But that is neither here nor there. The right protected, not granted or established, by the second amendment is said to belong to the "people" not to the militia. And that right "Shall not be infringed", which registration, licensing and all other the gun control nonesense certainly does, since "infringe" means to break in upon, even in the slightest amount. "Shall not be infringed", is much stronger than "shall not be violated" would have been, which is how the milder gun-controllers want to read the amendment.