Mansion, perhaps, with only one chair (4)
I believe the answer is:
seat
This could be a double definition.
'mansion' is the first definition.
(thesaurus)
'with only one chair' is the second definition.
'seat' can be an answer for 'chair' (something to sit on). I am not certain of the 'with only one' bit.
'perhaps' acts as a link.
Can you help me to learn more?
(Other definitions for seat that I've seen before include "See 10" , "Box ---, position of advantage" , "'A chair, say (4)'" , "Eg, chair, stool" , "Position (in parliament)" .)