Seat of empire (7)
I believe the answer is:
I believe this clue is a double definition.
'seat' is the first definition.
(ottoman is a kind of seat)
'of empire?' is the second definition.
(I've seen this before)
(Other definitions for ottoman that I've seen before include "that lacks arms and backing" , "item of furniture" , "Turk (historical); seat" , "Low upholstered seat - relating to a Turkish dynasty" , "Low, padded seat - Turkish empire" .)