<p><strong>Noun</strong></p><ul><li>the diameter of something of circular section, especially that of the inside of a tube: a pipe of three-inch caliber.</li><li>the diameter of the bore of a gun taken as a unit of measurement.</li><li>degree of capacity or competence; ability: a mathematician of high caliber.</li><li>degree of merit or excellence; quality: the high moral caliber of the era.</li></ul>