Monastic office's key books to return and send (9)
I believe the answer is:
abbotship
'monastic office's key books to return and send' is the definition.
I can't judge whether this defines the answer.
'key books to return and send' is the wordplay.
'key' becomes 'A' (musical key).
'books' becomes 'BB' (two abbreviations for book).
'return' says the letters should be written in reverse.
'and' says to put letters next to each other.
'send' becomes 'ship' (to send overseas).
'to' in reverse letter order is 'ot'.
'a'+'bb'+'ot'+'ship'='ABBOTSHIP'
Can you help me to learn more?
(Another definition for abbotship that I've seen is " monastery's post?".)