Capital where one is part of furniture (5)
I believe the answer is:
sofia
'capital' is the definition.
(capital of Bulgaria)
'where one is part of furniture' is the wordplay.
'where one' becomes 'i' (Roman numeral. I am not sure about the 'where' bit.).
'is part of' indicates putting letters inside (part of the inside).
'furniture' becomes 'sofa' (sofa is a kind of furniture).
'i' inserted inside 'sofa' is 'SOFIA'.
Can you help me to learn more?
(Other definitions for sofia that I've seen before include "capital city" , "European city" , "Balkan capital" , "seat of government" , "Foreign city" .)