A spring gun is a type of firearm that uses a spring mechanism to fire projectiles. However, there are a few synonyms for spring gun that might be useful to know. One of these is a pellet gun, which refers to a type of air gun that shoots pellets. Another synonym is a BB gun, which shoots small metal balls known as BBs. A third synonym is a slingshot, which is a handheld device used to shoot small, round projectiles such as stones or balls using a rubber band stretched between two prongs. Finally, a fourth synonym for a spring gun is an airgun, which is a type of firearm that uses compressed air to propel pellets or BBs.