Agreements initially missing for book (4)
I believe the answer is:
acts
'book' is the definition.
(book of the Bible)
'agreements initially missing' is the wordplay.
'agreements' becomes 'pacts' (pact is a kind of agreement).
'initially missing' means to remove the first letter.
'pacts' with its first letter taken away is 'ACTS'.
'for' is the link.
(Other definitions for acts that I've seen before include "performers for revue, say?" , "Biblical book" , "Things done" , "functions" , "placed before Romans?" .)