arm

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

• noun An upper limb of the human body, connecting the hand and wrist to the shoulder.
• noun A part similar to a human arm, such as the forelimb of an animal or a long part projecting from a central support in a machine.
• noun Something, such as a sleeve on a garment or a support on a chair, that is designed to cover or support the human arm.
• noun A relatively narrow extension jutting out from a large mass: synonym: branch.
• noun An administrative or functional branch, as of an organization.
• noun Power or authority.
• noun Sports The skill of throwing or pitching a ball well.
• idiom (an arm and a leg) An excessively high price.
• idiom (arm in arm) With arms linked together.
• idiom (at arm's length) At such a distance that physical or social contact is discouraged.
• idiom (with open arms) With great cordiality and hospitality.
• noun A weapon, especially a firearm.
• noun A branch of a military force.
• noun Warfare.
• noun Military service.
• noun Heraldry Bearings.
• noun Insignia, as of a state, an official, a family, or an organization.
• intransitive verb To supply or equip oneself with weaponry.
• intransitive verb To prepare oneself for warfare or conflict.
• intransitive verb To equip with weapons.
• intransitive verb To equip with what is needed for effective action.
• intransitive verb To provide with something that strengthens or protects.
• intransitive verb To prepare (a weapon or electronic system, such as an alarm) for use or operation, as by releasing a safety device.
• idiom (up in arms) Extremely upset; indignant.

from The Century Dictionary.

• To take by the arm; also, to seize or hold in the arms.
• noun In ordinary language: The upper limb of the human body, extending from the shoulder to the hand, and including the latter.
• noun The same, exclusive of the hand; the upper limb from the shoulder to the wrist. It is divided into upper arm, or arm proper, from the shoulder to the elbow, and lower arm, or forearm, from the elbow to the wrist.
• noun In human anatomy, the anterior extremity from the shoulder-joint to the elbow-joint, represented by the extent of the humerus; the brachium, as distinguished from the forearm or antebrachium.
• noun In comparative anatomy and zoology: The fore limb of any vertebrate, especially when terminating in a prehensile extremity like a hand, more or less removed from the office of locomotion; the pectoral or thoracic limb; the diverging appendage of the scapular arch or shoulder-girdle; a fore leg, wing, pectoral fin, etc.
• noun Some diverging or radiating part or organ like or likened to an arm, as the arm of a cephalopod, the wing of a pteropod, the brachium of a brachiopod, and the ray of a starfish, sand-star, or crinoid.
• noun Anything formed on the type of the arm, or resembling an arm in shape, position, or function.
• noun Figuratively, power; might; strength; authority: as, the secular arm.
• noun Hence That on which one relies for support or assistance; a prop; a stay.
• noun Milit.: A weapon.
• noun plural Armor; coverings for the body intended as defenses against weapons of war.
• noun A branch of the military service, as cavalry or artillery: as, the enemy was strong in artillery, but we were weak in that arm.
• noun Hence plural The use of weapons; military occupations; war.
• noun plural Deeds or exploits of war.
• noun In law, anything which a man takes in his hand in anger to strike or assault another.
• noun plural In botany, anything that serves as a defense to a plant, as prickles, thorns, or spines.
• noun plural In falconry, the legs of a hawk from the thigh to the foot.
• noun plural The heraldic bearings of an individual or a community, consisting of some device in heraldic tinctures (see tincture) borne on a shield, generally with the addition of a crest and sometimes with supporters.
• noun Synonyms Arm, Weapon. Arm is especially applied to those things which are designed for fighting and recognized as such; it includes means of defense as well as of offense. Weapon applies to any means of offense made for the purpose or (as a scythe, chisel, or hammer) used for the nonce.
• noun In violin-playing, the arm or its action in reference to the style of bowing: as, he plays with a good arm.
• noun In archery, the longitudinal half of a bow, extending from the handle to the end of the bowstaff: limb: classified as upper and lower arm, according to their relative position when the bow is held perpendicularly, as in shooting.
• noun At a disadvantage: as, to work at arm's length.
• To furnish or equip with weapons for offense or defense: as, to arm the militia.
• To cover or provide with whatever will add strength, force, or security: as, to arm the hilt of a sword; to arm a man-of-war with armor-plates.