This is the 722nd most frequent Finnish word.
historian
The Finnish word "historian" means "of history" or "the history" in English.
In this sentence, 'historian' is the possessive form of 'historia' and translates to 'of history'.
Hän on maailman historian tärkein henkilö.
He is the most important person in the history of the world.
Here, 'historian' refers to the exam for the subject 'history', and is in the genitive case.
Opiskelen historian tenttiä varten.
I am studying for the history exam.
In this usage, 'historian' is part of a compound indicating someone who researches history.