joint author vs writer

joint author and writer both are nouns.

Word	Noun	Adjective	Verb	Adverb
joint author	Yes	No	No	No
writer	Yes	No	No	No

As nouns, writer is a hypernym of joint author; that is, writer is a word with a broader meaning than joint author:

joint author: a writer who collaborates with others in writing something
writer: writes (books or stories or articles or the like) professionally (for pay)

Other hypernyms of joint author include author.

joint author (noun)	writer (noun)
a writer who collaborates with others in writing something	writes (books or stories or articles or the like) professionally (for pay)
	a person who is able to write and has written something