American Dictionary of the English Language

CUBIT, noun [Latin , the elbow; signifying a turn or corner; Gr.]

1. In anatomy, the fore arm; the ulna, and bone of the arm from the elbow to the wrist.

2. In mensuration, the length of a mans arm from the elbow to the extremity of the middle finger. The cubit among the ancients was of a different length among different nations. Dr. Arbuthnot states the Roman cubit at seventeen inches and four tenths; the cubit of the scriptures at a little less than 22 inches; and the English cubit at 18 inches.