The Collaborative International Dictionary of English v.0.48:
Duchy \Duch"y\ (d[u^]ch"[y^]), n.; pl. Duchies. [F. duch['e], OF. duch['e]e, (assumed) LL. ducitas, fr. L. dux. See Duke.] The territory or dominions of a duke; a dukedom. [1913 Webster]WordNet (r) 3.0 (2006):
duchy n 1: the domain controlled by a duke or duchess [syn: duchy, dukedom]