Reserve tome (4)
I believe the answer is:
book
I believe this clue is a double definition.
'reserve' is the first definition.
(to book something is to reserve it)
'tome' is the second definition.
(I've seen this before)
(Other definitions for book that I've seen before include "Show yellow card" , "Written work; reserve" , "Reading volume" , "Reserve (tickets)" , "Volume - maybe thrown at offender" .)