State's open society in retreat (5)
I believe the answer is:
syria
'state's' is the definition.
(Syria is an example)
'open society in retreat' is the wordplay.
'open' becomes 'airy' (both can mean spacious).
'society' becomes 's' (common abbreviation in names of organisations).
'in retreat' is a reversal indicator.
'airy'+'s'='airys'
'airys' reversed gives 'SYRIA'.
(Other definitions for syria that I've seen before include "Middle East republic" , "Mediterranean republic" , "Damascus is its capital city" , "In Mediterranean area" , "Eastern Mediterranean country" .)