incrustation vs tophus

incrustation and tophus both are nouns.

Word	Noun	Adjective	Verb	Adverb
incrustation	Yes	No	No	No
tophus	Yes	No	No	No

As nouns, tophus is a hyponym of incrustation; that is, tophus is a word with a more specific, narrower meaning than incrustation:

Other hyponyms of incrustation include calculus, tartar.

incrustation (noun)	tophus (noun)
a decorative coating of contrasting material that is applied to a surface as an inlay or overlay	an incrustation that forms on the teeth and gums
a hard outer layer that covers something	a deposit of urates around a joint or in the external ear; diagnostic of advanced or chronic gout
the formation of a crust