Capital investment that involves old penny (3,3)
I believe the answer is:
top hat
'capital investment that involves old penny' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'that involves old penny' is the wordplay.
'involves' means one lot of letters goes inside another.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'penny' becomes 'p' (short for pence).
'o'+'p'='op'
'that' enclosing 'op' is 'TOP-HAT'.
Can you help me to learn more?
(Other definitions for top hat that I've seen before include "Film starring Fred Astaire" , "Posh lid" , "It's seen with tails" , "Headgear (for those in tails?)" , "Stylish film" .)