Professor is a title given throughtout history to very learned people teaching to others usually at a university.
20th century
Ace referred to the Doctor as Professor.
51st century
River Song introduces herself as a Professor at a university. DW: Silence in the Library
100 trillion
In the year 100,000,000,000,000, Yana was given the tittle of Professor even their had been no universities for a century. DW: Utopia