Definition of: caliber

(kal′ə·bər) noun
1. The internal diameter of a tube.
2. Mil. a The internal diameter of the barrel of a gun, cannon, etc., expressed in decimals of an inch for small arms, millimeters for rifles, centimeters for cannon. b The diameter of a bullet, shell, etc. c The ratio of the length of a gun's bore to its diameter: a unit of length.
3. Degree of individual capacity or intellectual power; personal ability, quality, or worth. Also cal′i·bre. [<F calibre,? <Arabic qālib mold, form]