1) a cubit
2) a measure of length equal to distance from the joint of the elbow to the tip of the middle finger (i.e. about 18 inches, (.5 m) but its precise length varied and is disputed)
Part of Speech: noun masculine
Of uncertain affinity; the fore arm, that is, (as a measure) a cubit: - cubit.
These two sites give similar information, with the definition from several dictionaries and statistics on the use of the word.
Perseus Digital Library
University of Chicago's Logion lexicon
Thayer's dictionary plus other information.
From this site's dictionary (in Italian)
Click on the first column to search for that word as a form of the root πῆχυς; click on the second column to search for that grammatical form of the root πῆχυς; click on the third column to search for that word and grammatical form; click on the total to search for the root πῆχυς.