Book store? (5)
I believe this is a double definition.
'book' is the first definition.
(as in booking or reserving in advance)
'store' is the second definition.
(a reserve is a store or supply of something)
(Other definitions for reserve that I've seen before include "ice" , "Savings - book" , "Conservation area" , "Hold back" , "Husband - substitute" .)
(Other definitions for shelf that I've seen before include "Flat surface for holding objects" , "support for books?" , "Rock ledge; underwater bank" , "Works are held up by it" , "display" .)