nephritis vs kidney disease

nephritis and kidney disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
nephritis	Yes	No	No	No
kidney disease	Yes	No	No	No

As nouns, kidney disease is a hypernym of nephritis; that is, kidney disease is a word with a broader meaning than nephritis:

Other hypernyms of nephritis include nephropathy, nephrosis, renal disorder.

nephritis (noun)	kidney disease (noun)
an inflammation of the kidney	a disease affecting the kidneys