Is your question about the use of the word "militia" or the use of dictionaries?

If you're asking about militias, the dictionary.com definition is correct. In all the colonies, able-bodied men from the ages of 16 to 60 were typically required to join the county militia. Later on, this would change to the ages of 18 to 45, as the states became more populated and there were more young men available to serve. This would require them to go do training a few weekends each summer, and maybe a couple more weekends throughout the year. A 1647 Massachusetts law stipulated that militia men were to receive eight days of training every year. Some people were exempt from service, such as the clergy, Quakers, members of the legislature, and the infirm, but everybody else had to serve, or else they would be subject to legal punishments, such as jail time. In many cases, you couldn't hold public office unless you were a member of the militia, either. Because of the large number of men required to join, militia muster rolls are often used as census substitutes for research purposes, particularly before the U.S. Census began being conducted in 1790.

To more directly answer this question (if it is the question you're asking), another group that was exempt from militia duty were paid soldiers, such as those who joined up with Washington's Continental Army, or before that, those who had joined to serve alongside the British Army or Royal Navy, which would often happen during wartime--during one of the French and Indian Wars, for example. And then after that, this would have also included enlisted soldiers in the U.S. Army and Navy. There were active duty militias during times of war, but for the most part, the militias were reserve soldiers, only called up when the war front came close to their home county.

If you're asking about dictionaries, then the one that would have been most available to the founders was A Dictionary of the English Language by Samuel Johnson, first published in London in 1755. Noah Webster published his first provisional dictionary in 1806, under the title A Compendious Dictionary of the English Language, although it was his later 1828 dictionary, An American Dictionary of the English Language, that was his first comprehensive dictionary.

In the earlier 1806 dictionary, Webster wrote in the preface about Samuel Johnson's dictionary at length. It was clearly the standard by which English language dictionaries were compared to at the time. He also wrote in that preface a little about Nathan Bailey's An Universal Etymological English Dictionary first published in 1721. More briefly, Webster's preface mentioned Robert Lowth's Grammar published in 1762, and Thomas Sheridan's A General Dictionary of the English Language published in 1780.

Webster also mentioned dictionaries by several other writers, including Walker, Entick, Perry, Ash, and Jones, all published between 1775 and 1800. But these were all mainly pronunciation dictionaries, rather than definitional dictionaries, so Johnson's and Bailey's dictionaries were the most useful to Noah Webster when he began the long work to compiling his American dictionary.