Keep the above book page (8)
I believe the answer is:
preserve
'keep' is the definition.
(I know that keep can be written as preserve)
'above book page' is the wordplay.
'above' says to put letters next to each other (in a down clue, some letters go above others).
'book' becomes 're-serve' (as in booking or reserving in advance).
'page' becomes 'p'.
'reserve' put after 'p' is 'PRESERVE'.
'the' acts as a link.
(Other definitions for preserve that I've seen before include "Keep from decay, corpse or food" , "Prevent from deteriorating" , "Keep alive, maintain" , "Keep safe from spoilage" , "Keep - pickle - store" .)