Book shows self-restraint (7)
I believe the answer is:
reserve
This clue is a double definition.
'book' is the first definition.
(as in booking or reserving in advance)
'self-restraint' is the second definition.
(thesaurus)
'shows' is the link.
(Other definitions for reserve that I've seen before include "man on bench?" , "One on bench" , "Lack of openness" , "Bank" , "some distance" .)