Căl'i-ber or Căl'i-bre, n.
n. [Fr., Sp., & Pg. calibre, It. calibro, O. Fr. qualibre, from Lat. qua libra, of what pound, of what weight; applied first to the weight, and hence also to the diameter of the bullet, which determined again the diameter of the gun.]
Sense 1. (Gunnery.) The weight of a bullet, cannonball, or other projectile. [Obs.]
Sense 2. The diameter of the bore, as of a cannon or other fire-arm, or of any tube. “The caliber of empty tubes.” Reid.
A battery composed of three guns of small caliber. Prescott.
Sense 3. The diameter of a round body, as of a bullet or column.
Sense 4. (Fig.) Capacity or compass of mind. Burke.
Caliber-rule, gunner’s calipers, an instrument having a scale that is so divided, as that, the first part representing the diameter of an iron or leaden ball of one pound weight, the other parts are to the first as the diameters of balls of two, three, four, &c., pounds are to the diameter of a ball of one pound. It is used by engineers to determine, from a ball’s weight, its diameter, and vice versa.