Duchess

from WordNet (r) 3.0 (2006)

duchess
    n 1: the wife of a duke or a woman holding ducal title in her
         own right

from The Collaborative International Dictionary of English v.0.48

Duchess \Duch"ess\, n. [F. duchesse, fr. duc duke.]
   The wife or widow of a duke; also, a lady who has the
   sovereignty of a duchy in her own right.
   [1913 Webster]