firearm(n = noun.artifact) piece, small-arm - a portable gun; "he wore his firearm in a shoulder holster"
is a kind of gun
has parts: firing pin, lock, sights
has particulars: autoloader, self-loader, muzzle loader, handgun, pistol, shooting iron, side arm, repeater, repeating firearm, rifle, riot gun, scattergun, shotgun, smoothbore, .22, twenty-two
A gun, pistol, or any weapon from which a shot is discharged by the force of an explosive substance, as gunpowder. [1913 Webster]
firearm, n. (usu. in pl.) a gun, esp. a pistol or rifle.