eraser vs rubber eraser

eraser and rubber eraser both are nouns.

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

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

eraser: an implement used to erase something
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 hyponyms of eraser include blackboard eraser, ink eraser, pencil eraser, rubber.

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