A gun is not a weapon It's a tool Like a butcher's knife or a harpoon or an aligator?

In my opinion, you are absolutely correct. It is a tool or object THAT CAN be used as a weapon just as anything else, like for instance a pencil.

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A weapon is a tool used to cause harm. A gun has no intended purpose other than the causing of harm; it could conceivably be used as a makeshift hammer, I suppose, and some guns have tactical rails which can be used to attach sights and flashlights, but fundamentally, the purpose of a gun is to cause harm, or demonstrate the power of the bearer of the gun to harm others. Thus, a gun IS a tool, but also specifically a weapon.