Part of a bookcase (5)
I believe the answer is:
shelf
'part of a bookcase' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for shelf that I've seen before include "Protruding rock ledge" , "Projecting underwater ridge" , "Ledge for books etc" , "sort of life" , "A place to store" .)