Weapon n. : An instrument of offensive of defensive combat; something to fight with; anything used, or designed to be used, in destroying, defeating, or injuring an enemy, as a gun, a sword, etc.

Weapon n. : Fig.: The means or instrument with which one contends against another; as, argument was his only weapon.

Weapon n. : A thorn, prickle, or sting with which many plants are furnished.

Example:
What would be considered the smallest Weapon of mass destruction?

Taxonomy
weapons, target, projectiles, warfare, weaponry, infantry, firearms, sonic attack, free encyclopedia, spears, World War II, the enemy, fortification, Weapon development, weapon systems, doctrines, tactics, battles.

Defination from the web:
Weapon (disambiguation). See military technology and equipment for a comprehensive list of weapons and doctrines. ... Weapon Systems. Antique firearms. Gladius Scholarly journal on Ancient and Medieval Weapons ...