diameter vs caliber

diameter and caliber both are nouns.

Word	Noun	Adjective	Verb	Adverb
diameter	Yes	No	No	No
caliber	Yes	No	No	No

As nouns, caliber is a hyponym of diameter; that is, caliber is a word with a more specific, narrower meaning than diameter:

diameter: the length of a straight line passing through the center of a circle and connecting two points on the circumference
caliber: diameter of a tube or gun barrel

Other hyponyms of diameter include bore, calibre, gauge, windage.

diameter (noun)	caliber (noun)
the length of a straight line passing through the center of a circle and connecting two points on the circumference	a degree or grade of excellence or worth
a straight line connecting the center of a circle with two points on its perimeter (or the center of a sphere with two points on its surface)	diameter of a tube or gun barrel