refractivity vs deflexion

refractivity and deflexion both are nouns.

Word	Noun	Adjective	Verb	Adverb
refractivity	Yes	No	No	No
deflexion	Yes	No	No	No

As nouns, deflexion is a hypernym of refractivity; that is, deflexion is a word with a broader meaning than refractivity:

refractivity: the physical property of a medium as determined by its index of refraction
deflexion: the property of being bent or deflected

Other hypernyms of refractivity include bending, deflection.

refractivity (noun)	deflexion (noun)
the physical property of a medium as determined by its index of refraction	a turning aside (of your course or attention or concern)
	the property of being bent or deflected
	the amount by which a propagating wave is bent
	the movement of the pointer or pen of a measuring instrument from its zero position