Label describing each book leaves container (3,3)
I believe the answer is:
tea bag
'leaves container' is the definition.
(contains tea leaves)
'label describing each book' is the wordplay.
'label' becomes 'tag' ('tag' can be a synonym of 'label').
'describing' is an insertion indicator (describe can mean to form the outline of).
'each' becomes 'ea'.
'book' becomes 'b'.
'ea'+'b'='eab'
'tag' enclosing 'eab' is 'TEA-BAG'.
(Other definitions for tea bag that I've seen before include "wherewithal for a drink" , "Sachet to put in pot" , "Age bat (anag.)" , "One for the pot" , "Container for leaves" .)