noun (n)

• a degree or grade of excellence or worth(noun.attribute)

  Example:
  An executive of low caliber.
  

  Synonym:
  calibre, quality
  

  source: wordnet30
• diameter of a tube or gun barrel(noun.attribute)

  Synonym:
  bore, calibre, gauge
  

  source: wordnet30
• 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.(noun)

  source: webster1913