film writer vs scriptwriter

film writer and scriptwriter both are nouns.

Word	Noun	Adjective	Verb	Adverb
film writer	Yes	No	No	No
scriptwriter	Yes	No	No	No

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

film writer: someone who writes screenplays
scriptwriter: someone who writes scripts for plays or movies or broadcast dramas

film writer (noun)	scriptwriter (noun)
someone who writes screenplays	someone who writes scripts for plays or movies or broadcast dramas