An archduke was a prince who belonged to the old royal family of Austria — the Habsburgs. You did not earn the title; you were born into it. It sat above an ordinary duke, but it was an Austrian family rank, not a job in every European court. English speakers still know it mainly because of Archduke Franz Ferdinand, whose death in 1914 helped start the First World War. The title died with the Austrian empire after 1918, so today it belongs to history, not to living palaces. Though actually people mix it up with grand duke, which is a different title in other countries; both sound “higher than duke,” but they are not the same office. You may also meet archduchess for a woman of that house.