Cubit

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."

a measure used among the ancients. The Hebrews call it אמא, the mother of other measures: in Greek ϖῆχυς. A cubit originally was the distance from the elbow to the extremity of the middle finger: this is the fourth part of a well proportioned man’s stature. The common cubit is eighteen inches. The Hebrew cubit, according to Bishop Cumberland and M. Pelletier, is twenty-one inches; but others fix it at eighteen inches. The Talmudists observe, that the Hebrew cubit was larger by one quarter than the Roman. Lewis Capellus and others have asserted that there were two sorts of cubits among the Hebrews; one sacred, the other common; the sacred containing three feet, the common containing a foot and a half. Moses assigns to the Levites a thousand sacred cubits of land round about their cities, Num. xxxv, 4; and in the next verse he gives them two thousand common ones. The opinion, however, is very probable, that the cubit varied in different districts and cities, and at different times, &c.