historian vs scholar

historian and scholar both are nouns.

Word	Noun	Adjective	Verb	Adverb
historian	Yes	No	No	No
scholar	Yes	No	No	No

As nouns, scholar is a hypernym of historian; that is, scholar is a word with a broader meaning than historian:

historian: a person who is an authority on history and who studies it and writes about it
scholar: a learned person; someone who by long study has gained mastery in one or more disciplines

Other hypernyms of historian include bookman, scholarly person.

historian (noun)	scholar (noun)
a person who is an authority on history and who studies it and writes about it	a learned person; someone who by long study has gained mastery in one or more disciplines
	someone (especially a child) who learns (as from a teacher) or takes up knowledge or beliefs
	a student who holds a scholarship