index of refraction vs ratio

index of refraction and ratio both are nouns.

Word	Noun	Adjective	Verb	Adverb
index of refraction	Yes	No	No	No
ratio	Yes	No	No	No

As nouns, ratio is a hypernym of index of refraction; that is, ratio is a word with a broader meaning than index of refraction:

index of refraction: the ratio of the velocity of light in a vacuum to that in a medium
ratio: the relative magnitudes of two quantities (usually expressed as a quotient)

index of refraction (noun)	ratio (noun)
the ratio of the velocity of light in a vacuum to that in a medium	the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree
	the relative magnitudes of two quantities (usually expressed as a quotient)