pencil eraser vs rubber eraser

pencil eraser and rubber eraser both are nouns.

Word	Noun	Adjective	Verb	Adverb
pencil eraser	Yes	No	No	No
rubber eraser	Yes	No	No	No

As nouns, pencil eraser and rubber eraser are synonyms defined as:

pencil eraser and rubber eraser: an eraser made of rubber (or of a synthetic material with properties similar to rubber); commonly mounted at one end of a pencil

Other synonyms of pencil eraser include rubber.

pencil eraser (noun)	rubber eraser (noun)
an eraser made of rubber (or of a synthetic material with properties similar to rubber); commonly mounted at one end of a pencil	an eraser made of rubber (or of a synthetic material with properties similar to rubber); commonly mounted at one end of a pencil