birefringence vs refraction

birefringence and refraction both are nouns.

Word	Noun	Adjective	Verb	Adverb
birefringence	Yes	No	No	No
refraction	Yes	No	No	No

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

birefringence: splitting a ray into two parallel rays polarized perpendicularly
refraction: the change in direction of a propagating wave (light or sound) when passing from one medium to another

birefringence (noun)	refraction (noun)
splitting a ray into two parallel rays polarized perpendicularly	the amount by which a propagating wave is bent
	the change in direction of a propagating wave (light or sound) when passing from one medium to another