Cal·i·ber, Cal·ibre  n.
 1. Gunnery 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.   --Reid.
    A battery composed of three guns of small caliber.   --Prescott.
 Note: ☞ 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.
 2. The diameter of round or cylindrical body, as of a bullet or column.
 3. 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.

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 Cal·i·pers n. pl.  An instrument, usually resembling a pair of dividers or compasses with curved legs, for measuring the diameter or thickness of bodies, as of work shaped in a lathe or planer, timber, masts, shot, etc.; or the bore of firearms, tubes, etc.; -- called also caliper compasses, or caliber compasses.
 Caliper square, a draughtsman's or mechanic's square, having a graduated bar and adjustable jaw or jaws. --Knight.
 Vernier calipers. See Vernier.

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 Com·pass·es n., pl. An instrument for describing circles, measuring figures, etc., consisting of two, or (rarely) more, pointed branches, or legs, usually joined at the top by a rivet on which they move.
 Note: ☞ The compasses for drawing circles have adjustable pen points, pencil points, etc.; those used for measuring without adjustable points are generally called dividers. See Dividers.
 Bow compasses. See Bow-compass.
 Caliber compasses, Caliper compasses. See Calipers.
 Proportional, Triangular, etc., compasses. See under Proportional, etc.

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