grand-dukedom
/ˌɡran(d) ˈdjuːkdəm/ /ˌɡran(d) ˈdʒuːkdəm/noun
The territory of a Grand Duke or Duchess, a Grand Duchy; the office or dignity of a Grand Duke or Duchess (also personified).
Origin
Mid 17th century; earliest use found in 2nd Earl of Monmouth (1596–1661), translator. From grand + dukedom, after Grand Duke.