The Collaborative International Dictionary of English v.0.48:

Doublure \Dou`blure"\, n. [F.]
   1. (Bookbinding) The lining of a book cover, esp. one of
      unusual sort, as of tooled leather, painted vellum, rich
      brocade, or the like.
      [Webster 1913 Suppl.]

   2. (Paleon.) The reflexed margin of the trilobite carapace.
      [Webster 1913 Suppl.]