notepaper vs writing paper

notepaper and writing paper both are nouns.

Word	Noun	Adjective	Verb	Adverb
notepaper	Yes	No	No	No
writing paper	Yes	No	No	No

As nouns, writing paper is a hypernym of notepaper; that is, writing paper is a word with a broader meaning than notepaper:

notepaper: writing paper intended for writing short notes or letters
writing paper: paper material made into thin sheets that are sized to take ink; used for writing correspondence and manuscripts

notepaper (noun)	writing paper (noun)
writing paper intended for writing short notes or letters	paper material made into thin sheets that are sized to take ink; used for writing correspondence and manuscripts