an ancient unit of linear measure, about 18-22 inches (45.4-55.5 cm); orig., the length of the arm from the end of the middle finger to the elbow
Origin:
ME & OE < L cubitum, the elbow, cubit: for IE base see cube
See cubit in American Heritage Dictionary 4
cu·bit
noun
An ancient unit of linear measure, originally equal to the length of the forearm from the tip of the middle finger to the elbow, or about 17 to 22 inches (43 to 56 centimeters).
Origin: Middle English cubite, from Latin cubitum, cubit, elbow.