stationery vs letter paper

stationery and letter paper both are nouns.

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

As nouns, stationery and letter paper are synonyms defined as:

stationery and letter paper: paper cut to an appropriate size for writing letters; usually with matching envelopes

stationery (noun)	letter paper (noun)
paper cut to an appropriate size for writing letters; usually with matching envelopes	paper cut to an appropriate size for writing letters; usually with matching envelopes
	writing paper for use in writing correspondence