Flat as one overwhelmed by unsettled debts (6)
I believe the answer is:
bedsit
'flat' is the definition.
(I know that Bedsit is a type of flat)
'one overwhelmed by unsettled debts' is the wordplay.
'one' becomes 'i' (Roman numeral).
'overwhelmed by' indicates putting letters inside (inserted letters get absorbed or overwhelmed).
'unsettled' is an anagram indicator.
'debts' is an anagram of 'bedst'.
'i' inserted inside 'bedst' is 'BEDSIT'.
'as' acts as a link.
(Other definitions for bedsit that I've seen before include "Single room for living" , "Room to accommodate" , "Small flat" , "Cheap digs" , "little accommodation" .)