Koestler vs author

Koestler and author both are nouns.

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

Koestler (noun)	author (noun)
British writer (born in Hungary) who wrote a novel exposing the Stalinist purges during the 1930s (1905-1983)	writes (books or stories or articles or the like) professionally (for pay)
	someone who originates or causes or initiates something

Koestler (verb)	author (verb)
	be the author of