diametric vs diameter

diametric is not a noun while diameter is a noun.

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

diametric (noun)	diameter (noun)
	the length of a straight line passing through the center of a circle and connecting two points on the circumference
	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)

diametric (adjective)	diameter (adjective)
related to or along a diameter
characterized by opposite extremes; completely opposed