Private cabin, say, with revolving berth (9)
I believe the answer is:
stateroom
'private cabin' is the definition.
(I've seen this before)
'say with revolving berth' is the wordplay.
'say' becomes 'state' (synonyms).
'with' is a charade indicator (letters next to each other).
'revolving' says the letters should be written backwards.
'berth' becomes 'moor' (synonyms).
'moor' back-to-front is 'room'.
'state'+'room'='STATEROOM'
(Other definitions for stateroom that I've seen before include "part of palace" , "luxurious cabin" , "Place fit for a 27 [PRINCE]" , "Large private cabin on a ship" , "Passengers's private compartment on ship" .)