arm

noun

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 receiving 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.

A study arm of a clinical trial includes the active arm, which is the test product, a possible reference arm, which could be another active approved product, and a placebo arm.

—Anthony Sileno

armless

ˈärm-ləs 

adjective

armlike

ˈärm-ˌlīk 

adjective

see also:

arm in arm

Synonyms of arm

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

Examples of arm in a Sentence

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

Recent Examples on the Web

Victor Rivas, 40, sustained injuries to his arms and was treated at a hospital before he was booked into jail on allegations of driving while intoxicated, resisting arrest and being a fugitive from adjacent Jefferson Parish, Louisiana State Police said. —Dennis Romero, NBC news, 9 June 2026

Spurs phenom Victor Wembanyama also became a topic of discussion after standing with his arms folded during the national anthem before Game 1. —Alejandro Avila, FOXNews.com, 9 June 2026

In the background, in the doorway of a crumbling stone building, stands a tiny, faceless figure, her arms held neatly behind her back. —Literary Hub, 9 June 2026

Cue to the adorable Scooby-Doo excitedly jumping into Shaggy’s (Tanner Hagen) arms. —Denise Petski, Deadline, 8 June 2026

Word History

Etymology

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.

First Known Use

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

Phrases Containing arm

• an arm and a leg
• arm and a leg
• arm candy
• arm in arm
• 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

Old English earm "arm"

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 receiving 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