Left large-sized book in case (9)
I believe the answer is:
portfolio
'case' is the definition.
(portfolio is a kind of case)
'left large-sized book' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'large-sized book' becomes 'folio' (folio is a book size).
'port'+'folio'='PORTFOLIO'
'in' is the link.
(Other definitions for portfolio that I've seen before include "responsibility of minister" , "Range of investments" , "art collection" , "mixed dish" , "artist's sample work" .)