Capital one in seat for more than one (5)
I believe the answer is:
sofia
'capital' is the definition.
(capital of Bulgaria)
'one in seat for more than one' is the wordplay.
'one' becomes 'I' (Roman numeral).
'in' is an insertion indicator.
'seat for more than one' becomes 'sofa' (I can't justify this - if you can you should believe this answer much more).
'i' going into 'sofa' is 'SOFIA'.
Can you help me to learn more?
(Other definitions for sofia that I've seen before include "Balkan capital" , "European city" , "seat of government" , "capital place" , "Bulgarian capital" .)