ghostwriter vs author

ghostwriter and author both are nouns.

Word	Noun	Adjective	Verb	Adverb
ghostwriter	Yes	No	No	No
author	Yes	No	Yes	No

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

ghostwriter: a writer who gives the credit of authorship to someone else
author: writes (books or stories or articles or the like) professionally (for pay)

Other hypernyms of ghostwriter include writer.

ghostwriter (noun)	author (noun)
a writer who gives the credit of authorship to someone else	writes (books or stories or articles or the like) professionally (for pay)
	someone who originates or causes or initiates something

ghostwriter (verb)	author (verb)
	be the author of