baroness

from WordNet (r) 3.0 (2006)

baroness
    n 1: a noblewoman who holds the rank of baron or who is the wife
         or widow of a baron

from The Collaborative International Dictionary of English v.0.48

Baroness \Bar"on*ess\, n.
   A baron's wife; also, a lady who holds the baronial title in
   her own right; as, the Baroness Burdett-Coutts.
   [1913 Webster]