Book-keep (7)
I believe the answer is:
reserve
I believe this clue is a double definition.
'book' is the first definition.
(synonyms)
'keep' is the second definition.
(reserving is a kind of keeping)
(Other definitions for reserve that I've seen before include "Bank" , "put to one side" , "not in the front line" , "Twelfth man < 's coolness" , "Book - substitute player" .)