kidney stone vs nephrolith

kidney stone and nephrolith both are nouns.

Word	Noun	Adjective	Verb	Adverb
kidney stone	Yes	No	No	No
nephrolith	Yes	No	No	No

As nouns, kidney stone and nephrolith are synonyms defined as:

Other synonyms of kidney stone include renal calculus, urinary calculus.

kidney stone (noun)	nephrolith (noun)
a calculus formed in the kidney	a calculus formed in the kidney