shelfback

plural shelfbacks

1. The vertical surface forming the back of a shelf.

   She came home later that day from Mrs. Rafferty's with a blue platter, which she placed standing up against the shelfback in the linen closet.

   2001, Regina McBride, The Nature of Water and Air, page 62

2. The spine of a book.

   There was the man who collected any old volumes on etymology. There was a collector of books with gilded Victorian shelfbacks.

   1934, The Atlantic Monthly, volume 153, page 71