What is Weapon?

Legal Definition
A weapon, arm, or armament is any device used with intent to inflict damage or harm to living beings, structures, or systems. Weapons are used to increase the efficacy and efficiency of activities such as hunting, crime, law enforcement, self-defense, and warfare. In a broader context, weapons may be construed to include anything used to gain a strategic, material or mental advantage over an adversary.

While just about any ordinary objects such as sticks, stones, cars, or pencils can be used as weapons, many are expressly designed for the purpose – ranging from simple implements such as clubs, swords and guns, to complicated modern intercontinental ballistic missiles, biological and cyberweapons. Something that has been re-purposed, converted, or enhanced to become a weapon of war is termed weaponized, such as a weaponized virus or weaponized lasers.
-- Wikipedia
Legal Definition
An instrument used in fighting; an instrument of offensive or defensive combat. The term is chiefly used, in law, in the statutes prohibiting the carrying of "concealed" or "deadly" weapons. See those titles.
-- Black's Law Dictionary
Legal Definition
An instrument of offensive or defensive combat; something to fight with. See 81 Wis. 239, 29 Am. St. Rep. 891, 51 N. W. 437.
-- Ballentine's Law Dictionary