Doctor vs theologian

Doctor and theologian both are nouns.

Word	Noun	Adjective	Verb	Adverb
Doctor	Yes	No	No	No
theologian	Yes	No	No	No

As nouns, theologian is a hypernym of Doctor; that is, theologian is a word with a broader meaning than Doctor:

Doctor: (Roman Catholic Church) a title conferred on 33 saints who distinguished themselves through the orthodoxy of their theological teaching
theologian: someone who is learned in theology or who speculates about theology

Other hypernyms of Doctor include theologiser, theologist, theologizer.

Doctor (noun)	theologian (noun)
(Roman Catholic Church) a title conferred on 33 saints who distinguished themselves through the orthodoxy of their theological teaching	someone who is learned in theology or who speculates about theology