weapon

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. An instrument of attack or defense in combat, as a gun, missile, or sword.
2. n. Zoology A part or organ, such as a claw or stinger, used by an animal in attack or defense.
3. n. A means used to defend against or defeat another: Logic was her weapon.
4. v. To supply with weapons or a weapon; arm.

Century Dictionary and Cyclopedia

1. n. Any instrument of offense; anything used, or designed to be used, in attacking an enemy, as a sword, a dagger, a club, a rifle, or a cannon.
2. n. Any object, particular, or instrumentality that may be of service in a contest or struggle, or in resisting adverse circumstances, whether for offense or defense; anything that may figuratively be classed among arms.
3. n. In zoology, any part or organ of the body which is or may be used as a means of attack or defense, as horns, hoofs, claws, spurs, stings, spines, teeth, electric organs, etc.; an arm or armature. Synonyms See arm.
4. To arm with weapons.

Wiktionary

1. n. An instrument of attack or defense in combat or hunting, e.g. most guns, missiles, or swords.
2. n. An instrument or other means of harming or exerting control over another.

GNU Webster's 1913

1. 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.
2. n. Fig.: The means or instrument with which one contends against another.
3. n. (Bot.) A thorn, prickle, or sting with which many plants are furnished.

WordNet 3.0

1. n. a means of persuading or arguing
2. n. any instrument or instrumentality used in fighting or hunting