crust vs tophus

crust and tophus both are nouns.

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

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

Other hyponyms of crust include calculus, tartar.

crust (noun)	tophus (noun)
the trait of being rude and impertinent; inclined to take liberties	an incrustation that forms on the teeth and gums
the outer layer of the Earth	a deposit of urates around a joint or in the external ear; diagnostic of advanced or chronic gout
a hard outer layer that covers something

crust (verb)	tophus (verb)
form a crust or form into a crust