arm

1 of 5

noun (1)

ˈärm 

plural arms

1

: a human upper limb

especially : the part between the shoulder and the wrist

2

: something like or corresponding to an arm: such as

a

: the forelimb of a vertebrate

b

: a limb of an invertebrate animal

c

: a branch or lateral shoot of a plant

d

: a slender part of a structure, machine, or an instrument projecting from a main part, axis, or fulcrum

e

: the end of a ship's yard

also : the part of an anchor from the crown to the fluke see anchor illustration

f

: any of the usually two parts of a chromosome lateral to the centromere

3

: an inlet of water (as from the sea)

4

: a narrow extension of a larger area, mass, or group

5

: power, might

the long arm of the law

6

: a support (as on a chair) for the elbow and forearm

7

: sleeve

8

: the ability to throw or pitch a ball well

also : a player having such ability

9

: a functional division of a group, organization, institution, or activity

the logistical arm of the air force

10

medical : a group of subjects provided a particular treatment in a clinical trial

Since this trial did not include a radiation-only treatment arm, it has been questioned whether radiation therapy alone might be as effective as sequential chemotherapy and radiation therapy in preserving the larynx.

—Everett E. Vokes et al.

armless

ˈärm-ləs 

adjective

armlike

ˈärm-ˌlīk 

adjective

arm

2 of 5

verb

armed; arming; arms

transitive verb

1

: to furnish or equip with weapons

2

: to furnish with something that strengthens or protects

arming citizens with the right to vote

3

: to equip or ready for action or operation

arm a bomb

intransitive verb

: to prepare oneself for struggle or resistance

arm for combat

arm

3 of 5

noun (2)

often attributive

1

a

: a means (such as a weapon) of offense or defense

especially : firearm

b

: a combat branch (as of an army)

c

: an organized branch of national defense (such as the navy)

2

arms plural

a

: the hereditary heraldic devices of a family

b

: heraldic devices adopted by a government

3

arms plural

a

: active hostilities : warfare

a call to arms

b

: military service

Arm

4 of 5

abbreviation (1)

Armenian

ARM

5 of 5

abbreviation (2)

adjustable rate mortgage

Phrases

arm in arm

: with arms linked together

up in arms

: aroused and ready to undertake a fight or conflict

Synonyms

Noun (1)

• department
• agency
• office
• bureau
• desk
• service

Noun (2)

• gun
• firearm
• rifle

Examples of arm in a Sentence

Noun (1)

a company that needs to beef up its marketing arm if it wants to compete in today's business world

this arm of the Atlantic is surprisingly peaceful, as the stronger ocean currents do not reach this far

Maine has so many long, narrow arms that jut out into the ocean that early coastal settlers found it much easier to travel by sea

few criminals manage to permanently escape the long arm of the law

Verb

They armed the men for battle.

The group of fighters was armed by a foreign government.

The two countries have been arming themselves for years, but now they have agreed to disarm.

We armed ourselves with the tools we would need to survive in the forest.

They arm people with accurate information.

arming women with the right to vote

Once the bomb has been armed, we have five minutes to escape.

Noun (2)

soldiers grabbing their arms and helmets and heading into battle

Recent Examples on the Web

Noun

Trump’s predecessors feared that strikes on Iran’s nuclear facilities, regardless of their tactical success, could give Tehran the political justification to withdraw from the Nuclear Nonproliferation Treaty and openly pursue nuclear arms, driving its program further underground and out of sight. —Michael Wilner, Los Angeles Times, 26 June 2025

Make sure to check spray arms and filters regularly for clogs and mineral deposits. —Brandee Gruener, Southern Living, 26 June 2025

Verb

Assuming that your definition of just fine includes being open to attack by anyone armed with an exploit for the latest security vulnerabilities. —Davey Winder, Forbes.com, 27 June 2025

The government sent hundreds of F.B.I. agents, U.S. marshals, and others to the Wounded Knee trenches, armed with military equipment including armored personnel carriers and tear gas. —Nick Estes, New Yorker, 26 June 2025

Word History

Etymology

Noun (1)

Middle English, going back to Old English earm, arm, going back to Germanic *arma-, masculine, (whence also Old Frisian erm "arm," Old Saxon arm, Old High German aram, arm, Old Norse armr, Gothic arms), going back to Indo-European *h₂orH-mo-, whence also Old Church Slavic ramo "shoulder," Bosnian-Croatian-Serbian rȁme, stem rȁmen-, Czech ráměk; a parallel zero-grade *h₂r̥H-mó- gives Old Prussian irmo "arm," Lithuanian (eastern dialects) ìrmėdė "pain from gout, chill, fever" (irm- "arm" + -ėdė "eating"), Sanskrit īrmá- "arm," Avestan arəma-; Latin armus "forequarter (of an animal), shoulder" probably goes back to *h₂erH-mo-

Note: Usually claimed to be a derivative of the verb *h₂er- "fit, join" (see arm entry 3)—very plausible semantically—though the Sanskrit and Baltic forms require a second laryngeal (*h₂erH-) in the base (cf. Rix et al., Lexikon der indogermanischen Verben, 2. Auflage, Wiesbaden, 2001, where the verbal base is posited without a second laryngeal). Could the suffix be *-H-mo-? The Slavic noun fluctuates in inflection between -mo- and -men- (see André Vaillant, Grammaire comparée des langues slaves, II:1 [Lyon, 1958], pp. 214-15). According to P. Schrijver, The Reflexes of the Proto-Indo-European Laryngeals in Latin (Amsterdam, 1991), p. 194, Latin armus cannot be traced to *h₂r̥H-mo-, which would have yielded *ramus. Regarding Armenian armukn "elbow," see H. K. Martirosyan, Etymological Dictionary of the Armenian Inherited Lexicon, Leiden, 2010, s.v.

Verb

Middle English armen, borrowed from Anglo-French armer, going back to Latin armāre, derivative of arma "implements of war, weapons, equipment" — more at arm entry 3

Noun (2)

Middle English armes (plural), "weapons, the military profession, heraldic devices," borrowed from Anglo-French, plural of arme "weapon," going back to Latin arma (neuter plural) "implements of war, weapons, equipment," derivative, with a suffix *-mo-, from a presumed verbal base *ar-, going back to Indo-European *h₂er- "fit, join," whence Greek reduplicated aorist ḗraron "(I) fit together, equipped, fit closely" (from which present tense ararískō, ararískein), ármenos (middle participle) "fitting, suited to," and (with suffixed *-smo- giving initial aspiration?) harmós "joint," hárma, harmat- "chariot, team of horses"; Armenian arari "(I) made," aṙnem "I make"

Note: See also art entry 1, arthro-, article entry 1, artiodactyl.

First Known Use

Noun (1)

before the 12th century, in the meaning defined at sense 1

Verb

13th century, in the meaning defined at transitive sense 2

Noun (2)

13th century, in the meaning defined at sense 1a

Phrases Containing arm

• an arm and a leg
• arm and a leg
• arm candy
• arm's length
• arm-twisting
• arm wrestling
• as long as your/my arm
• at arm's length
• chance one's arm
• cost an arm and a leg
• keep (someone or something) at arm's length
• one-arm bandit
• on one's arm
• put the arm on
• rocker arm
• roll-over arm
• shot in the arm
• small arm
• stiff-arm
• straight-arm
• strong-arm
• the long arm of the law
• twist one's arm
• twist someone's arm

Rhymes for arm

• charm
• farm
• harm
• alarm
• disarm
• forearm
• gendarme
• nonfarm
• rearm
• firearm
• underarm

Kids Definition

arm

1 of 3 noun

ˈärm 

1

a

: a human upper limb

especially : the part between the shoulder and wrist

b

: a corresponding limb of a lower vertebrate animal

2

: something resembling an arm in shape or position

an arm of the sea

the arm of a chair

3

: power entry 1 sense 1a

the long arm of the law

4

: sleeve sense 1

armed

ˈärmd

adjective

armless

ˈärm-ləs 

adjective

armlike

-ˌlīk 

adjective

arm

2 of 3 verb

1

: to provide with weapons

arm a regiment

2

: to provide with a way of fighting, competing, or succeeding

armed herself with facts

3

: to make ready for action or use

arm a bomb

arm

3 of 3 noun

1

a

: weapon

especially : firearm

b

: a branch of an army

c

: a branch of the military forces

2

plural : the designs on a shield or flag of a family or a government

3

plural

a

: actual fighting : warfare

a call to arms

b

: military service

Etymology

Noun

Old English earm "arm"

Noun

Middle English armes "weapons," from early French armes (same meaning), from Latin arma "weapons" — related to alarm see Word History at alarm

Medical Definition

arm

noun

ˈärm 

1

a

: a human upper limb

b

: the part of the human upper limb between the shoulder and the wrist

also : brachium

2

a

: the forelimb of a vertebrate other than a human being

b

: a limb of an invertebrate animal

c

: any of the usually two parts of a chromosome lateral to the centromere

3

: a group of subjects provided a particular treatment in a clinical trial

Since this trial did not include a radiation-only treatment arm, it has been questioned whether radiation therapy alone might be as effective as sequential chemotherapy and radiation therapy in preserving the larynx.

—Everett E. Vokes et al., The New England Journal of Medicine

Legal Definition

ARM

abbreviation

adjustable rate mortgage