historian vs bookman

historian and bookman both are nouns.

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

As nouns, bookman is a hypernym of historian; that is, bookman 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
bookman: a learned person; someone who by long study has gained mastery in one or more disciplines

Other hypernyms of historian include scholar, scholarly person.

historian (noun)	bookman (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