Capital firm banking capital, right? (5)
I believe the answer is:
cairo
'capital' is the definition.
(capital of Egypt)
'firm banking capital right?' is the wordplay.
'firm' becomes 'co' (abbreviation for company).
'banking' means one lot of letters goes inside another.
'capital' becomes 'AI' (resembles 'A1', old-fashioned term for excellent).
'right?' becomes 'r' (abbreviation).
'ai'+'r'='air'
'co' going around 'air' is 'CAIRO'.
(Other definitions for cairo that I've seen before include "Port upstream from the Nile delta" , "African city" , "North African capital" , "Capital city on the Nile" , "Egyptian capital" .)