1. an ancient unit of length based on the length of the forearm;
The Collaborative International Dictionary of English v.0.48:
Cubit \Cu"bit\ (k[=u]"b[i^]t), n. [L. cubitum, cubitus; elbow,
ell, cubit, fr. (because the elbow serves for leaning upon)
cubare to lie down, recline; cf. Gr. ky`biton elbow, ky`ptein
to bend, stoop, kyfo`s bent, stooping, humpbacked. Cf.
1. (Anat.) The forearm; the ulna, a bone of the arm extending
from elbow to wrist. [Obs.]
2. A measure of length, being the distance from the elbow to
the extremity of the middle finger.
Note: The cubit varies in length in different countries, the
Roman cubit being 17.47 inches, the Greek 18.20, the
Hebrew somewhat longer, and the English 18 inches.
WordNet (r) 3.0 (2006):
n 1: an ancient unit of length based on the length of the
Easton's 1897 Bible Dictionary:
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."