writer vs speller

writer and speller both are nouns.

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

As nouns, speller is a hyponym of writer; that is, speller is a word with a more specific, narrower meaning than writer:

writer (noun)	speller (noun)
writes (books or stories or articles or the like) professionally (for pay)	an introductory textbook to teach spelling
a person who is able to write and has written something	someone who spells words