Left paper in briefcase (9)
I believe the answer is:
portfolio
'briefcase' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'left paper' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'paper' becomes 'folio' (folio is a kind of paper).
'port'+'folio'='PORTFOLIO'
'in' is the link.
Can you help me to learn more?
(Other definitions for portfolio that I've seen before include "minister's office" , "Minister's responsibility" , "Large case" , "Cabinet responsibility" , "Set of papers" .)