The seat of a former empire (7)
I believe the answer is:
ottoman
I believe this is a double definition.
'the seat' is the first definition.
(ottoman is a kind of seat)
'a former empire' is the second definition.
(I've seen this in another clue)
'of' is the link.
(Other definitions for ottoman that I've seen before include "Am not to (anag)" , "Chest padded as seat" , "Low, padded seat - Turkish empire" , "Turkish dynasty and cushioned stool" , "Long, low seat - Turkish" .)