Cal"i*ber, Cal"ibre (?), n. [F. calibre, perh. fr. L. qualibra of what pound, of what weight; hence, of what size, applied first to a ball or bullet; cf. also Ar. qalib model, mold. Cf. Calipers, Calivere.]
The diameter of the bore, as a cannon or other firearm, or of any tube; or the weight or size of the projectile which a firearm will carry; as, an 8 inch gun, a 12-pounder, a 44 caliber.
The caliber of empty tubes.
A battery composed of three guns of small caliber.
The caliber of firearms is expressed in various ways. Cannon are often designated by the weight of a solid spherical shot that will fit the bore; as, a 12-pounder; pieces of ordnance that project shell or hollow shot are designated by the diameter of their bore; as, a 12 inch mortar or a 14 inch shell gun; small arms are designated by hundredths of an inch expressed decimally; as, a rifle of .44 inch caliber.
The diameter of round or cylindrical body, as of a bullet or column.
Fig.: Capacity or compass of mind.
Caliber compasses. See Calipers. -- Caliber rule, a gunner's calipers, an instrument having two scales arranged to determine a ball's weight from its diameter, and conversely. -- A ship's caliber, the weight of her armament.
© Webster 1913.