It holds books account together (6)
I believe the answer is:
intact
'together' is the definition.
(I've seen this in another clue)
'it holds books account' is the wordplay.
'holds' means one lot of letters goes inside another.
'books' becomes 'NT' (New Testament).
'account' becomes 'ac' (abbreviation).
'nt'+'ac'='ntac'
'it' enclosing 'ntac' is 'INTACT'.
(Other definitions for intact that I've seen before include "Not broken or damaged" , "Undiminished" , "Unscathed" , "Whole and undamaged" , "Complete - undamaged" .)