An Etymological Dictionary of the German Language/Annotated/Arm
Arm, masculine, ‘arm, branch,’ from the equivalent Middle High German arm, Old High German aram, arm, masculine; a word common to the Teutonic group; compare Old Saxon arm, Dutch arm, Anglo-Saxon earm, English arm, Old Icelandic armr, Gothic arms, masculine, ‘arm.’ Like many terms for parts of the body (see Arsch, Fuß, Herz, Knie, Nagel, &c.), Arm extends beyond the Teutonic dialects. It is. primitively related to Latin armus, ‘the topmost part of the upper arm, fore-quarter’ (Greek ἁρμός, ‘suture, joint, shoulder,’ belongs to another division), Old Bulgarian ramę, ‘shoulder, arm,’ Sanscrit îrmá-s, masculine, ‘fore-quarter, arm.’ See Ermel.