essayist vs author

essayist and author both are nouns.

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

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

essayist: a writer of literary works
author: writes (books or stories or articles or the like) professionally (for pay)

Other hypernyms of essayist include writer.

essayist (noun)	author (noun)
a writer of literary works	writes (books or stories or articles or the like) professionally (for pay)
	someone who originates or causes or initiates something

essayist (verb)	author (verb)
	be the author of