stationery vs writing paper

stationery and writing paper both are nouns.

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

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

stationery: paper cut to an appropriate size for writing letters; usually with matching envelopes
writing paper: paper material made into thin sheets that are sized to take ink; used for writing correspondence and manuscripts

stationery (noun)	writing paper (noun)
paper cut to an appropriate size for writing letters; usually with matching envelopes	paper material made into thin sheets that are sized to take ink; used for writing correspondence and manuscripts