Meaning of caliber

cal•i•ber

1. the diameter of something of circular section, esp. that of the inside of a tube: a pipe of three-inch caliber.
2. the diameter of the bore of a gun taken as a unit of measurement.
3. degree of capacity or competence; ability: a mathematician of high caliber.
4. degree of merit or excellence; quality: the high moral caliber of the era.