Put back nearly all the bits of the bookcase? (6)
I believe the answer is:
shelve
'put back' is the definition.
(both can mean to cancel or postpone)
'nearly all the bits of the bookcase?' is the wordplay.
'nearly all' means to remove the last letter.
'the bits of the bookcase?' becomes 'shelves' (a bookcase has shelves).
'shelves' with its final letter removed is 'SHELVE'.
(Other definitions for shelve that I've seen before include "Postpone" , "Provide space for books" , "Put off indefinitely" , "Put on one 1 down" , "Slope gently" .)