The word historian is a noun because a noun is a person, place, thing, idea, or quality. A historian is a person
The word painting can be a noun as in a piece of art. It can also be a verb where it is the present participle of paint.
historian
"Painter" is a noun. If a word ends in "-er" and the preceding letters spell a verb, the original word is almost always an "agency" noun.
Henry Adams
You can become an Art historian, Philanthropist, a Curator, work in art conservation or finish an education degree to teach art history at University
John L. O'Sullivan
You tell the history of ur class...duuh :P
part of speech
The part of speech for this particular word is a noun.
what part of speech is beneath
adverb
The part of speech for "answer" is a noun.
The part of speech for "lecturer" is a noun.
The part of speech for "breezy" is an adjective.
The part of speech for "buried" is a verb.
The part of speech for "rapid" is an adjective.
The part of speech for "indefinite" is an adjective.