The Collaborative International Dictionary of English v.0.48:
Archduchess \Arch`duch"ess\, n. [Pref. arch- + duchess.] The consort of an archduke; also, a princess of the imperial family of Austria. See Archduke. [1913 Webster]WordNet (r) 3.0 (2006):
archduchess n 1: a wife or widow of an archduke or a princess of the former ruling house of Austria