hard rubber vs ebonite

hard rubber and ebonite both are nouns.

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

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

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

Other synonyms of hard rubber include vulcanite.

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