Back of a book (5)
I believe the answer is:
spine
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">back of a book</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for spine that I've seen before include "Vertebral column" , "Part of book's jacket" , "Part of a book" , "Strength of character" , "Line of vertebrae" .)