In the end, not finishing book (5)
I believe the answer is:
atlas
'book' is the definition.
(atlas is a kind of book)
'in the end not finishing' is the wordplay.
'in the end' becomes 'at last' (synonyms).
'not finishing' means to remove the last letter.
'atlast' with its last letter taken away is 'ATLAS'.
(Other definitions for atlas that I've seen before include "He had the world on his shoulders" , "Book of maps or charts" , "collection of charts" , "Titan - map book" , "The first cervical vertebra" .)