1) a sack
1a) a receptacle for holding or carrying various things, as money, food, etc.
1b) a course cloth, a dark course stuff made especially from the hair of animals
1c) a garment of the like material, and clinging to the person like a sack, which was wont to be worn (or drawn over the tunic instead of the cloak or mantle) by mourners, penitents, suppliants and also by those who like the Hebrew prophets, lead an austere life
Part of Speech: noun masculine
Citing in TDNT: 7:56, 995
Of Hebrew origin [H8242]; "sack" cloth, that is, mohair (the material or garments made of it, worn as a sign of grief): - sackcloth.
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 σάκκος; click on the second column to search for that grammatical form of the root σάκκος; click on the third column to search for that word and grammatical form; click on the total to search for the root σάκκος.