Private cabin, say, with space (9)
I believe the answer is:
stateroom
'private cabin' is the definition.
(I've seen this before)
'say with space' is the wordplay.
'say' becomes 'state' (synonyms).
'with' is a charade indicator (letters next to each other).
'space' becomes 'room' (enough space or room to do something).
'state'+'room'='STATEROOM'
(Other definitions for stateroom that I've seen before include "Private cabin on board ship" , "Passengers's private compartment on ship" , "Large private cabin on a ship" , "Luxury cabin on a liner" , "Place fit for a 27 [PRINCE]" .)