: 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.—👁 Image 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.—👁 Image Anthony Sileno
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
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Noun
Crew has an amazing sight in store Four days later during the lunar flyby, the moon will appear to be the size of a basketball held at arm’s length.—👁 Image Marcia Dunn, Chicago Tribune, 2 Apr. 2026 Hilda Lorena Cifuentes Cifuentes family photo Cifuentes suffered extensive injuries to her face, arms, legs and abdomen, along with head trauma.—👁 Image Tori Mason, CBS News, 2 Apr. 2026
Verb
The Falls at Willow Creek Apartments were on lockdown as SWAT negotiated with the suspect, who was armed with a knife and sword, according to the Folsom Police Department.—👁 Image Kayla Moeller, CBS News, 30 Mar. 2026 Ghazali, armed with a rifle, allegedly rammed a vehicle into Temple Israel, one of the nation’s largest Reform Jewish synagogues.—👁 Image Andrew Stanton, MSNBC Newsweek, 30 Mar. 2026 See All Example Sentences for arm
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"
: 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.—👁 Image Everett E. Vokes et al., The New England Journal of Medicine
