What does archduke mean?
The definition of archduke
Arch`duke”, n.
Etym: [Pref. arch- + duke.]

A prince of the imperial family of Austria.

Note: Formerly this title was assumed by the rulers of Lorraine, Brabant, Austria, etc. It is now appropriated to the descendants of the imperial family of Austria through the make line, all such male descendants being styled archduke, and all such female descendants archduchesses.