diarist vs writer

diarist and writer both are nouns.

Word	Noun	Adjective	Verb	Adverb
diarist	Yes	No	No	No
writer	Yes	No	No	No

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

diarist (noun)	writer (noun)
someone who keeps a diary or journal	writes (books or stories or articles or the like) professionally (for pay)
	a person who is able to write and has written something