Work that is about making capital investment (3,3)
I believe the answer is:
top hat
'work that is about making capital investment' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'work that is about' is the wordplay.
'work' becomes 'op' (abbreviation for opus).
'is about' is an insertion indicator.
'op' put within 'that' is 'TOP-HAT'.
Can you help me to learn more?
(Other definitions for top hat that I've seen before include "Formal headgear of lofty sort" , "Formal attire" , "Formal head-wear for a man" , "Film with Astaire and Rogers" , "Fancy lid" .)