A weapon is an instrument used with the aim of causing harm or death to human being — and for inflicting damage upon civil or military infrastructure and life-sustaining natural resources. In essence, it is a tool made with the purpose of increasing the efficacy and efficiency of such activities as hunting, fighting, the committing of criminal acts, the preserving of law and order, and the waging of war.
Weapons are employed individually or collectively and can be improvised or purpose-built, sometimes with great skill and ingenuity. They range from simple implements such as clubs through to complicated modern machines such as intercontinental ballistic missiles.
In a broader context, weapons may be construed to include anything used to gain a strategic, material or mental advantage over an adversary on land, sea, air, or even outer space.
Source: Wikipedia
