cal·i·ber 
(kălə-bər)
(kălə-bər)n.
1.
a. The diameter of the inside of a round cylinder, such as a tube.
b. The diameter of the bore of a firearm, usually shown in hundredths or thousandths of an inch and expressed in writing or print in terms of a decimal fraction: .45 caliber.
c. The diameter of a large projectile, such as an artillery shell, measured in millimeters or in inches.
2. Degree of worth; quality: a school of high caliber; an executive of low caliber.
[French calibre, from Italian calibro, from Arabic qālib, qālab, mold, shoe tree, from Greek kālapous, shoemaker's last : kālon, wood + pous, foot; see ped- in the Appendix of Indo-European roots.]