An 'arms storehouse' is a place where weapons are kept. There are a number of synonyms that can be used to describe a place where arms are stored. These include 'arsenal', 'weaponry', 'ammunition depot', 'armory', or 'military base'. Each of these terms evokes a different sense of the kind of place being described. For example, 'arsenal' suggests a large, well-stocked facility, while 'weaponry' or 'ammunition depot' may imply a more specific focus on guns or bullets, respectively. 'Armory' conjures up images of a medieval castle, while 'military base' suggests a more modern facility, used for weapons storage as well as training and operations.