the.com/firearm

means A weapon that fires a projectile using an explosive charge, typically gunpowder — rifles, pistols, and shotguns all qualify.

from Simply compound: 'fire,' because igniting a charge is how it works, plus 'arm' in the old sense of a weapon (from Latin 'arma,' the gear of war). The word shows up as firearms moved past earlier 'fire' weapons like fire-lances and hand cannons, needing a general term for anything that launched its shot by combustion rather than a blade or a bow.