The
Duchy of Prussia (, ) or
Ducal Prussia (German:
Herzogliches Preußen, Polish:
Prusy Ksiazece) was a
duchy in eastern
Prussia established during the
Protestant Reformation in 1525. It was the first
Lutheran duchy with a dominant German-speaking population, as well as
Polish and
Lithuanian minorities. In old texts and in Latin, the term
Prut(h)enia refers alike to
Ducal Prussia, its western neighbor
Royal Prussia, and their common predecessor,
Teutonic Prussia. The adjectival form of the name was "
Prut(h)enic".