A gun is a kind of projectile weapons that fire bullets.
Background[]
Silver bullets can kill or injure witches, and other evil creatures (werewolves and other Were Folk, Vampires and Lizard Folk). Graham could not shoot Dahlia as he did not have a gun on him.
Behind the scenes[]
A similar technology would be cannons. Pirates often had cannons on their Pirate Ships. The pirates who sailed the Western Sea had 'gun ports' on the side of the ship, but strangely no noticeable cannons.
The reference to possible guns and cannons, and certain other technology would seem to indicate that King's Quest exists in a steampunk like universe.
The earliest handheld firearms appeared around 15th century in Asia and Middle-East. The first cannons introduced into Europe were probably used in Iberia, during the Christian wars against Muslims in the 13th century; their use was also first documented in the Middle East around this time.