Politician is in the capital of Italy supporting company settlement (10)
I believe the answer is:
compromise
'settlement' is the definition.
(compromise is a kind of settlement)
'politician is in the capital of italy supporting company' is the wordplay.
'politician' becomes 'mp'.
'in the' means one lot of letters goes inside another.
'capital of italy' becomes 'rome' ('Rome' can be a synonym of 'capital of italy').
'supporting' is a charade indicator (letters next to each other) (in a down clue, some letters go below others).
'company' becomes 'co' (abbreviation).
'is' inserted into 'rome' is 'romise'.
'mp'+'romise'='mpromise'
'mpromise' put after 'co' is 'COMPROMISE'.
(Other definitions for compromise that I've seen before include "accommodation" , "Agree a middle way" , "Middle course" , "Settle by concession" , "Trade-off" .)