hard rubber vs vulcanite

hard rubber and vulcanite both are nouns.

Word	Noun	Adjective	Verb	Adverb
hard rubber	Yes	No	No	No
vulcanite	Yes	No	No	No

As nouns, hard rubber and vulcanite are synonyms defined as:

hard rubber and vulcanite: a hard nonresilient rubber formed by vulcanizing natural rubber

Other synonyms of hard rubber include ebonite.

hard rubber (noun)	vulcanite (noun)
a hard nonresilient rubber formed by vulcanizing natural rubber	a hard nonresilient rubber formed by vulcanizing natural rubber