Spare book (7)
I believe the answer is:
reserve
This clue is a double definition.
'spare' is the first definition.
(synonyms)
'book' is the second definition.
(as in booking or reserving in advance)
(Other definitions for reserve that I've seen before include "ice" , "Hold back" , "Set aside - shyness" , "Lack of openness" , "Book - spare player" .)