An arm is a limb on the upper part of a person's body. You can call the front limb of any animal an arm, though they're more often called "legs."

Starfish have five arms, while humans have two. The sleeves of your shirt are arms too, and an excellent baseball pitcher is said to have "an arm," meaning a powerful throw. When arm is a verb, it means "supply with weapons." These meanings have two different roots: an arm with a hand on the end comes from the Old English earm, while the weapon arm is rooted in the Latin arma, or "weapons."

Definitions of arm
  1. noun
    a human limb; technically the part of the superior limb between the shoulder and the elbow but commonly used to refer to the whole superior limb
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    type of:
    one of the jointed appendages of an animal used for locomotion or grasping: arm; leg; wing; flipper
  2. noun
    the part of a garment that is attached at the armhole and that provides a cloth covering for the arm
    synonyms: sleeve
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    dolman sleeve
    a sleeve with a large armhole and tight cuff
    long sleeve
    a sleeve extending from shoulder to wrist
    raglan sleeve
    a sleeve that extends in one piece to the neckline of a coat or sweater with seams from the armhole to the neck
    the sleeve of a shirt
    short sleeve
    a sleeve extending from the shoulder to the elbow
    type of:
    cloth covering
    a covering made of cloth
  3. noun
    the part of an armchair or sofa that supports the elbow and forearm of a seated person
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    writing arm
    an arm of a tablet-armed chair; widened to provide a writing surface
    type of:
    a support for the arm
  4. noun
    any projection that is thought to resemble a human arm
    “the arm of the record player”
    “an arm of the sea”
    synonyms: branch, limb
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    type of:
    any structure that branches out from a central support
  5. noun
    a division of some larger or more complex organization
    synonyms: branch, subdivision
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    local post office, post office
    a local branch where postal services are available"
    Executive Office of the President, executive branch
    the branch of the United States government that is responsible for carrying out the laws
    legislative branch
    the branch of the United States government that has the power of legislating
    judicial branch
    the branch of the United States government responsible for the administration of justice
    type of:
    an administrative unit in government or business
  6. noun
    any instrument or instrumentality used in fighting or hunting
    synonyms: weapon, weapon system
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    the legendary sword of King Arthur
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    a weapon for shooting arrows, composed of a curved piece of resilient wood with a taut cord to propel the arrow
    bow and arrow
    a weapon consisting of arrows and the bow to shoot them
    brass knuckles, brass knucks, knuckle duster, knuckles, knucks
    a small metal weapon; worn over the knuckles on the back of the hand
    fire ship
    a weapon consisting of a ship carrying explosives that is set adrift to destroy enemy ships
    a weapon that squirts ignited fuel for several yards
    a weapon that discharges a missile at high velocity (especially from a metal tube or barrel)
    a weapon with a handle and blade with a sharp point
    light arm
    a rifle or pistol
    a rocket carrying a warhead of conventional or nuclear explosives; may be ballistic or directed by remote control
    medieval weapon consisting of a spearhead attached to a long pole or pikestaff; superseded by the bayonet
    missile, projectile
    a weapon that is forcibly thrown or projected at a targets but is not self-propelled
    a weapon (a sword or dagger) used for slashing
    a simple weapon consisting of a looped strap in which a projectile is whirled and then released
    lance, shaft, spear
    a long pointed rod used as a tool or weapon
    stun baton, stun gun
    a weapon designed to disable a victim temporarily by delivering a nonlethal high-voltage electric shock
    blade, brand, steel, sword
    a cutting or thrusting weapon that has a long metal blade and a hilt with a hand guard
    hatchet, tomahawk
    weapon consisting of a fighting ax; used by North American Indians
    W.M.D., WMD, weapon of mass destruction
    a weapon that kills or injures civilian as well as military personnel (nuclear and chemical and biological weapons)
    Greek fire
    a mixture used by Byzantine Greeks that was often shot at adversaries; catches fire when wetted
    air gun, air rifle, airgun
    a gun that propels a projectile by compressed air
    air-to-air missile
    a missile designed to be launched from one airplane at another
    air-to-ground missile, air-to-surface missile
    a missile designed to be launched from an airplane at a target on the ground
    ack-ack, ack-ack gun, antiaircraft, antiaircraft gun, flack, flak, pom-pom
    artillery designed to shoot upward at airplanes
    a projectile with a straight thin shaft and an arrowhead on one end and stabilizing vanes on the other; intended to be shot from a bow
    assagai, assegai
    the slender spear of the Bantu-speaking people of Africa
    a sword with only one cutting edge
    ballistic missile
    a missile that is guided in the first part of its flight but falls freely as it approaches target
    a knife that can be fixed to the end of a rifle and used as a weapon
    bioarm, biological weapon, bioweapon
    any weapon usable in biological warfare
    boomerang, throw stick, throwing stick
    a curved piece of wood; when properly thrown will return to thrower
    a gun that is loaded at the breech
    a sword with a broad blade and (usually) two cutting edges; used to cut rather than stab
    bullet, slug
    a projectile that is fired from a gun
    heavy automatic gun fired from an airplane
    heavy gun fired from a tank
    cannon ball, cannonball, round shot
    a solid projectile that in former times was fired from a cannon
    cavalry sword, saber, sabre
    a stout sword with a curved blade and thick back
    chemical weapon
    chemical substances that can be delivered using munitions and dispersal devices to cause death or severe harm to people and animals and plants
    a bow fixed transversely on a wooden stock grooved to direct the arrow (quarrel)
    Cupid's bow
    a curved bow with reversed curve ends
    cutlas, cutlass
    a short heavy curved sword with one edge; formerly used by sailors
    dagger, sticker
    a short knife with a pointed blade used for piercing or stabbing
    a small narrow pointed missile that is thrown or shot
    a short broad slightly convex medieval sword with a sharp point
    fencing sword
    a sword used in the sport of fencing
    firearm, piece, small-arm
    a portable gun
    gas gun
    a gun that fires gas shells
    guided missile
    a rocket-propelled missile whose path can be controlled during flight either by radio signals or by internal homing devices
    a pike fitted with an ax head
    a bow drawn by hand as distinguished from a crossbow
    heat-seeking missile
    a missile with a guidance system that directs it toward targets emitting infrared radiation (as the emissions of a jet engine)
    a spear thrown as a weapon or in competitive field events
    a curved steel knife with a razor-sharp edge used in combat by the Gurkhas; has cultural and religious significance in Nepal
    a powerful wooden bow drawn by hand; usually 5-6 feet long; used in medieval England
    machete, matchet, panga
    a large heavy knife used in Central and South America as a weapon or for cutting vegetation
    minute gun
    (military) gun that is discharged once every minute (usually as part of a military funeral)
    atomic weapon, nuclear weapon
    a weapon of mass destruction whose explosive power derives from a nuclear reaction
    partisan, partizan
    a pike with a long tapering double-edged blade with lateral projections; 16th and 17th centuries
    Quaker gun
    a dummy gun or piece of artillery made usually of wood
    rapier, tuck
    a straight sword with a narrow blade and two edges
    a missile equipped with a device that is attracted toward some kind of emission (heat or light or sound or radio waves)
    set gun, spring gun
    a gun that is set to fire on any intruder that comes in contact with the wire that sets it off
    a knife used as a weapon
    pellet, shot
    a solid missile discharged from a firearm
    air-to-air missile with infrared homing device
    a projectile made by chewing a piece of paper and shaping it into a sphere
    trench knife
    a knife with a double-edged blade for hand-to-hand fighting
    a spear with three prongs
    a kind of pike used by foot soldiers in the 14th century
    whaling gun
    a gun (or device resembling a gun) for discharging a projectile (especially a harpoon) at a whale
    a long Turkish knife with a curved blade having a single edge
    high explosive
    a powerful chemical explosive that produces gas at a very high rate
    type of:
    a device that requires skill for proper use
  7. verb
    prepare oneself for a military confrontation
    synonyms: build up, fortify, gird
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    demilitarise, demilitarize, disarm
    remove offensive capability from
    re-arm, rearm
    arm anew
    arm in advance of a confrontation
  8. verb
    supply with arms
    “The U.S. armed the freedom fighters in Afghanistan”
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    supply with weapons
    arm again
    type of:
    furnish, provide, render, supply
    give something useful or necessary to
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