1610s, modeled on French archiduchesse; see arch- "chief" + duchess. In later use generally "a princess of the reigning family of Austria," translating German Erzherzogin. Compare archduke, which is the masc. form.
also archi-, word-forming element meaning "chief, principal; extreme, ultra; early, primitive," from Latinized form of Greek arkh-, arkhi- "first, chief, primeval," combining form of arkhos "a chief, leader, commander," arkhein "be first, begin" (see archon).
"female sovereign of a duchy; consort or widow of a duke," c. 1300, from Old French duchesse, from Late Latin or Medieval Latin ducissa, fem. of dux "duke" (see duke (n.)). Often spelled dutchess until early 19c. (as in Dutchess County, New York, U.S.).
1520s, from French archeduc (Modern French archiduc), from Merovingian Latin archiducem (c. 750); see arch- + duke (n.). Formerly the title of the rulers of Austrasia, Lorraine, Brabant, and Austria; later the titular dignity of the sons of the Emperor of Austria. Related: Archducal; archduchy.
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Definitions of archduchess from WordNet
a wife or widow of an archduke or a princess of the former ruling house of Austria;