Complete set of books embraced by European republic (6)
I believe the answer is:
entire
'complete' is the definition.
(synonyms)
'set of books embraced by european republic' is the wordplay.
'set of books' becomes 'NT' (New Testament).
'embraced by' means one lot of letters goes inside another.
'european republic' becomes 'eire' (Irish name for Ireland).
'nt' placed into 'eire' is 'ENTIRE'.
(Other definitions for entire that I've seen before include "Envelope" , "Unharmed - total" , "Whole - undamaged" , "in one piece" , "everything" .)