An armory is a special military building where weapons and ammunition are kept. In the old days, when an army needed more cannon balls, it would retrieve them from an armory.
An armory is an important part of a military's assets, since it stores arms and equipment and is also sometimes the place where soldiers are trained to use them. Another way to use the noun armory is to refer to a stockpile or stash of non-military goods. You might talk about, for example, your armory of cupcake recipes or your armory of perfectly sharpened pencils. The Latin root, arma, means "weapons."