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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