Merriam-Webster Collegiate Dictionary - caliber

 or calibre  noun  Etymology: Middle French calibre, from Old Italian calibro, from Arabic qalib shoemaker's last  Date: 1567  1.  a. degree of mental capacity or moral quality  b. degree of excellence or importance  2.  a. the diameter of a bullet or other projectile  b. the diameter of a bore of a gun usually expressed in hundredths or thousandths of an inch and typically written as a decimal fraction .32 ~  3. the diameter of a round or cylindrical body; especially the internal diameter of a hollow cylinder