Source : Webster's Revised Unabridged Dictionary (1913)

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.

Source : WordNet®

duchy
     n : the domain controlled by a duke or duchess [syn: {dukedom}]