1911 Encyclopædia Britannica/Elbow

ELBOW, in anatomy, the articulation of the humerus, the bone of the upper arm, and the ulna and radius, the bones of the forearm (see Joints). The word is thus applied to things which are like this joint in shape, such as a sharp bend of a stream or river, an angle in a tube, &c. The word is derived from the O. Eng. elnboga, a combination of eln, the forearm, and boga, a bow or bend. This combination is common to many Teutonic languages, cf. Ger. Ellbogen. Eln still survives in the name of a linear measure, the “ell,” and is derived from the O. Teut. alina, cognate with Lat. ulna and Gr. ὠλένη, the forearm. The use of the arm as a measure of length is illustrated by the uses of ulna, in Latin, cubit, and fathom.