1. A historic unit of distance frequently mentioned in the Bible and other ancient sources; traditionally the length between the tip of the middle finger and the crux of the elbow of an adult male: Mr. Jones, the archeologist, used the ancient cubit to measure the distance between the wall and the gate to the garden.
2. Etymology: from Latin cubitum, "the elbow"; related to cubare, "to lie down, be lying"; that is, "on which someone lies in a reclining position.

An ancient unit of measure based on the forearm from elbow to fingertip, usually from eighteen to twenty-two inches. Such a measure, known by a word meaning "forearm" or the like, was known to many people; such as, Greek pekhys and Hebrew ammah.

The unit represents the length of a man's forearm from his elbow to the tip of his outstretched middle finger. This distance tends to be about eighteen inches or roughly forty-five centimeters in length.

In ancient times, the cubit was usually defined as equal to twenty-four digits or six English system, the digit is conventionally identified as 3/4 inch; this makes the ordinary cubit exactly 18 inches (45.72 centimeters).

The Roman cubit was shorter, about 44.4 centimeters (17.5 inches). The ordinary Egyptian cubit was just under 45 centimeters, and most authorities estimate the royal cubit at about 52.35 centimeters (20.61 inches).