the diameter of something of circular section, esp. that of the inside of a tube

a pipe of three-inch caliber.

Ordnance . the diameter of the bore of a gun taken as a unit of measurement.

degree of capacity or competence; ability

a mathematician of high caliber.

degree of merit or excellence; quality

the high moral caliber of the era.

noun

ability , appetency , capability , competence , constitution , dignity , distinction , endowment , essence , faculty , force , gifts , habilitation , merit , nature , parts , power , quality , scope , stature , strength , talent , value , virtue , worth , worthiness , bore , class , diameter , gauge , grade , length , measure , measurement , striking power , weight , capacity , character , degree , prestige , prominence , rank , skill