Adorn country mansion where the "King" lived (9)
I believe the answer is:
graceland
'mansion where the king lived' is the definition.
(home of Elvis Presley aka The King)
'adorn country' is the wordplay.
'adorn' becomes 'grace' (synonyms).
'country' becomes 'land' (synonyms).
'grace'+'land'='GRACELAND'
(Other definitions for graceland that I've seen before include "Elvis Presley's home" , "Paul Simon album" , "Elvis shrine" , "The King's residence" .)