D defs.my
Entry 3 senses Webster, 1913

Caliber

/kăl'-əb-ẽr/ · Cal·i·ber · IPA /ˈkæl.ə.bɚ/
01 n. 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;…
  1. 1.
    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.(Gunnery)
    “The caliber of empty tubes.” — Reid.
    “A battery composed of three guns of small caliber.” Prescott.
  2. 2.
    The diameter of round or cylindrical body, as of a bullet or column.
  3. 3.
    Fig.: Capacity or compass of mind.
Phrases & compounds
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.