Heb. 'ammah; i.e., "mother of the arm," the fore-arm, is a word derived from the Latin cubitus, the lower arm. It is difficult to determine the exact length of this measure, from the uncertainty whether it included the entire length from the elbow to the tip of the longest finger, or only from the elbow to the root of the hand at the wrist. The probability is that the longer was the original cubit. The common computation as to the length of the cubit makes it 20.24 inches for the ordinary cubit, and 21.888 inches for the sacred one. This is the same as the Egyptian measurements.
A rod or staff the measure of a cubit is called in Judg. 3:16 _gomed_, which literally means a "cut," something "cut off." The LXX. and Vulgate render it "span."