1. Bear Arms. "To bear arms is, in itself, a military term. One does not bear arms against a rabbit. The phrase simply translates the Latin arma ferre. The infinitive ferre, to bear, comes from the verb fero. The plural noun arma explains the plural usage in English ('arms'). One does not 'bear arm.' Latin arma is, etymologically, war 'equipment,' and it has no singular forms. By legal and other channels, arma ferre entered deeply into the European language of war. To bear arms is such a synonym for waging war that Shakespeare can call a just war 'just-borne arms' and a civil war 'self-borne arms.' Even outside the phrase 'bear arms,' much of the noun’s use alone echoes Latin phrases: to be under arms (sub armis), the call to arms (ad arma), to follow arms (arma sequi), to take arms (arma capere), to lay down arms (arma ponere). 'Arms' is a profession that one brother chooses as another chooses law or the church. An issue undergoes the arbitrament of arms. In the singular, English 'arm' often means a component of military force (the artillery arm, the cavalry arm)
[...]
2. To keep. Gun advocates read 'to keep and bear' disjunctively, and think the verbs refer to entirely separate activities. 'Keep,' for them, means 'possess personally at home'— a lot to load into one word. To support this entirely fanciful construction, they have to neglect the vast literature on militias. It is precisely in that literature that to-keep-and-bear is a description of one connected process. To understand what 'keep' means in a military context, we must recognize how the description of a local militia’s function was always read in contrast to the role of a standing army. Armies, in the ideology of the time, should not be allowed to keep their equipment in readiness." [...]
In America, the Articles of Confederation required that "every state shall always keep up a well regulated and disciplined militia sufficiently armed and accoutred shall provide and constantly ready for use, in public stores, number of field pieces and tents, a proper quantity of arms, ammunition and equipage" (equipage being etymological sense of arma). Thus is as erroneous to suppose that "keep" means, of itself, "keep at home" as to think that "arms" means only guns. Patrick Henry tells us, the militia's arms include "regimentals, etc."˜ flags, ensigns, engineering tools, siege apparatus, and other "accoutrements of war.
Some arms could be kept at home, course. Some officers kept their most valuable piece of war equipment, a good cross-country horse, at home, where its upkeep was a daily matter feeding and physical regimen. But military guns were not ideally kept home. When militias were armed, it was, so far as possible, with guns standard issue, interchangeable parts, uniform in their shot, upkeep and performance— the kind of "firelocks" Trenchard wanted kept "in every parish" (not every home)[.]"
http://www.potowmack.org/garwills.html