peeress

noun

1. A noblewoman married to a peer.

   “But there were more than a score of peers there beside, with their peeresses in tall feathers, diamonds, and monstrous hoops.”

2. A woman holding a noble title in her own right.

   “[I]t is obvious that the Californian heiress is not the only gainer by an alliance which will enable her to make the easy and common transition from a Republican lady to a British peeress.”