Definition of "peeress"

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

1863, Sheridan Le Fanu, The House by the Churchyard

… 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.

1892, Sir Arthur Conan Doyle, “The Noble Bachelor”, in The Adventures of Sherlock Holmes‎, HTML edition, The Gutenberg Project, published 2011