Servant's part of a book (4)
I believe the answer is:
page
I believe this is a double definition.
'servant's' is the first definition.
(page can mean a boy servant)
'part of a book' is the second definition.
(I've seen this in another clue)
(Other definitions for page that I've seen before include "Leaf - boy attendant" , "Sheet of book" , "Attendant - sheet" , "Young male attendant" , "servant-boy" .)