1911 Encyclopædia Britannica/Arm

ARM (a common Teutonic word; the Indo-European root is ar, to join or fit; cf. the Lat. armus, shoulder, and the plural word arma, weapons, Gr. ἁρμός, joint, and the reduplicated ἀραρίσκειν, to join), the human upper limb from the shoulder to the wrist, and the fore limb of an animal. (See Anatomy: Superficial and Artistic, and Skeleton: Appendicular.) The word is also used of any projecting limb, as of a crane, or balance, of a branch of a tree, and so, in a transferred sense, of the branch of a river or a nerve. Through the Fr. armes, from the Lat. arma, and so in English usually in the plural “arms,” comes the use of the word for weapons of offence and defence, and in many expressions such as “men-at-arms,” “assault-at-arms,” and the like, and for the various branches, artillery, cavalry, infantry, of which an army is composed, the “arms of the service.” “Arms” or “armorial bearings” are the heraldic devices displayed by knights in battle on the defensive armour or embroidered on the surcoat worn over the armour and hence called “coats of arms.” These became hereditary and thus are borne by families, and similar insignia are used by nations, cities, episcopal sees and corporations generally. (See Heraldry.)