Other forms: arms
Your arm is the long part of your body between shoulder and hand. Break your arm, arm in arm, hold out your arm.
An arm is also a branch of an organisation — the political arm, the armed forces — and a projecting part: the arm of a chair, the arm of a record player. As a verb, to arm is to supply with weapons, which is a separate word from Latin arma. Note at arm's length, meaning at a deliberate distance; twist somebody's arm; and cost an arm and a leg.
1nounarmThe part of the body between shoulder and hand.
“She broke her arm when she fell off her bike.”
2nounbranchA branch of an organisation, or a projecting part.
“The company's charity arm gives money to local schools.”
Too few real examples of this word to estimate which sense is commonest.
arm is a limb or branch.
Old English earm comes from a root meaning a joint or fitting — the same source as Latin armus, a shoulder. The weapon sense is a different Latin word, arma, and the two collided in English.
Proto-Indo-European
*h₂er-
Middle English
arm
English, today
arm
Built from
From Middle English arm. From Middle English arm, from Old English earm (Anglian arm), from Proto-West Germanic arm, from Proto-Germanic armaz (“arm”), from Proto-Indo-European h₂r̥mós (“a fitting, joint; arm, forequarter”), a suffixed form of h₂er- (“to join, fit together”). 2
Etymology from Wiktionary, CC BY-SA