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\ ˈärm 
\ 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
6 : a support (as on a chair) for the elbow and forearm
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. arm in arm : with arms linked together
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
1a : 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
up in arms : aroused and ready to undertake a fight or conflict
History and Etymology for arm
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"
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Time Traveler for arm
The first known use of arm was before the 12th century
See more words from the same century