weapon

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An instrument of attack or defense in combat, as a gun, missile, or sword.
• noun Zoology A part or organ, such as a claw or stinger, used by an animal in attack or defense.
• noun A means used to defend against or defeat another.
• transitive verb To supply with weapons or a weapon; arm.

from The Century Dictionary.

• To arm with weapons.
• noun 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.
• noun 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.
• noun 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.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.
• noun Fig.: The means or instrument with which one contends against another.
• noun (Bot.) A thorn, prickle, or sting with which many plants are furnished.
• noun See under Concealed.
• noun [Obs.] a salve which was supposed to cure a wound by being applied to the weapon that made it.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a means of persuading or arguing
• noun any instrument or instrumentality used in fighting or hunting