1. The diameter of the bore of a gun or the diameter of a bullet or shell.
Usage: Often used in military or firearms contexts
2. The degree of excellence or importance of a person or thing; quality or ability.
Usage: Figurative use; common in formal writing

Examples

• The rifle fires bullets of .308 calibre.
• Different calibres of ammunition are used for different purposes.
• She is a musician of the highest calibre.
• The company only hires engineers of exceptional calibre.
• The debate featured speakers of considerable calibre.
• These weapons come in various calibres suitable for different tasks.