What is a…
cubit
Hebrew: אַמָּה —transliteration: ammah —meaning: “mother of the arm,” the fore-arm; an “ell” (“ell” as in elbow; a measurement originally based on the length of the forearm)
The word “cubit” is derived from the Latin cubitus—meaning the lower arm.
It is difficult to determine the exact length of this measure in Biblical times, due partly to 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 [51.40959999999999 centimeters] for the ordinary cubit, and 21.888 inches [55.59552 centimeters] for the sacred one. This is the same as the ancient Egyptian measurements.
The likely minimum length is about 18 inches or 45 cm.
Short cubit
A rod or staff the measure of a cubit is called in Judges 3:16 גֹּמֶד ( transliteration: gomed ), which literally means a “cut,” something “cut off.” The Septuagint and Vulgate translate it as “span.” It is believed to represent a short cubit (from elbow to knuckles of clenched fist).
More information