Reserves
'reserves' is the definition.
(booking is a kind of reserving)
This is the entire clue.
(Other definitions for books that I've seen before include "Tomes, volumes" , "Reserve tickets" , "Reserves" , "See 1" .)
(Another definition for nestegg that I've seen is " savings".)
'reserves' is the definition.
('set aside' can be a synonym of 'reserve')
This is all the clue.
(Another definition for sets aside that I've seen is " Places in reserve for now, like asses diet".)