That is
a definition of militia but of course, that isn't the definition the United States uses (this has all been discussed on these forums before).
Now, we know from the writings of several of the founding fathers of what they had in mind with the second amendment and it mostly disagrees with your suggestion, but let's for the sake of argument assume that the second amendment refers strictly to "militia."
Well let's look at US legal code. The
Militia Act of 1792 defined
the militia (as opposed to a dictionary definition of a militia) as "every free able-bodied white male citizen between the ages of 18 and 45." It even described the weapons and gear that it required these citizens to own.
Now let's fast-forward to 1903 which saw the
Militia Act of 1903 passed. This is the act that created the modern day National Guard however this act also created another militia called the "unorganized militia" or "reserve militia" which is the same able-bodied male citizen" (Including blacks now. See? Progress!) and is very much in line with the traditional meaning of the term as used in the United States.
There is some interesting history surrounding this particular law. Do you know why it was written? It has nothing to do with firearm rights or even a need for a National Guard. During the civil war there was a great deal of confusion over federal army forces and state militias which were little more than private armies controlled by state governors. Often it was unclear who these units answered to on the battlefield. This act created a true National Guard, raised by each state but that ultimately answered to the federal government.
But why the separation between "organized" and unorganized" militias? Return to the wording of the Militia Act of 1792 for a bit. It essentially meant that every man in the described age group was by definition a conscript in the state militia, was subject to training and also was required to provide their own equipment. By the 1900's most men simply didn't want to be bothered with the burden of training and maintaining equipment (most already didn't, in violation of the law), thus a legal separation was created. You were either paid militia (National Guard) or unorganized militia (everyone else). This law is still on the books today. So to the non-military (non-senile) men of this forum who are US citizens and who fall between the ages of 18 and 45, in case you didn't know, you are part of an unofficial army of the United States.
Of course all of this silly legalese that crops up every time there is a shooting is a pointless exercise. Those of you who have a problem with firearms are welcome to try to change the constitution at any time. Of course that requires you go through that pesky democratic process thing... Hmmm... Well, as this country has proven time and time again, there are plenty of ways to get around democracy.