vellum vs writing paper

vellum and writing paper both are nouns.

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

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

vellum: a heavy creamy-colored paper resembling parchment
writing paper: paper material made into thin sheets that are sized to take ink; used for writing correspondence and manuscripts

vellum (noun)	writing paper (noun)
fine parchment prepared from the skin of a young animal e.g. a calf or lamb	paper material made into thin sheets that are sized to take ink; used for writing correspondence and manuscripts
a heavy creamy-colored paper resembling parchment