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Webster 1913 Edition

Noun.

The wife of a peer; a woman ennobled in her own right, or by right of marriage.

Noun.

The consort of a peer; a noble lady.

peeress ‎(plural peeresses)

A noblewoman married to a peer
A woman holding a noble title in her own right.
- 1892, Sir Arthur Conan Doyle, “The Noble Bachelor”, in The Adventures of Sherlock Holmes, HTML edition, The Gutenberg Project, published 2011:
  … it 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.