Column in the back of a book! (5)
I believe the answer is:
spine
I believe this clue is a double definition.
'column' is the first definition.
(I have seen 'Vertebral column ' mean 'spine' so perhaps 'column' could also mean 'spine')
'the back of a book' is the second definition.
(I've seen this in another clue)
'in' acts as a link.
(Other definitions for spine that I've seen before include "Backbone" , "Vertebrae, complete" , "Vertebral column" , "Part of a book" , "Thorn" .)