Hard section of a textbook, perhaps (5)
I believe the answer is:
spine
(Other definitions for spine that I've seen before include "Strength of character" , "Thorn" , "Part of a book" , "Vertebral column" , "Series of vertebrae" .)
I believe the answer is:
spine
(Other definitions for spine that I've seen before include "Strength of character" , "Thorn" , "Part of a book" , "Vertebral column" , "Series of vertebrae" .)