The title of Archduke (feminine: Archduchess) (German: Erzherzog, feminine form: Erzherzogin) is a rank above Duke and under King. It is very rare. It was used only by princes of the House of Habsburg.
The English word is recorded only since 1530, derived from Middle Latin archidux, from arch(i)- (see arch- (adj.)) + dux 'duke' .