Book in reverse order (7)
I believe the answer is:
reserve
'book' is the definition.
(as in booking or reserving in advance)
'reverse order' is the wordplay.
'order' indicates anagramming the letters.
'reverse' with letters rearranged gives 'RESERVE'.
'in' is the link.
(Other definitions for reserve that I've seen before include "8 [RESTRAINT]" , "Order" , "not in the front line" , "put to one side" , "man on bench?" .)