Last aria Rameau finally composed for land down under (9)
I believe the answer is:
australia
'land down under' is the definition.
'last aria rameau finally composed' is the wordplay.
'finally' suggests the final letters.
'composed' indicates an anagram.
The final letter of 'rameau' is 'u'.
'last'+'aria'+'u'='lastariau'
'lastariau' is an anagram of 'AUSTRALIA'.
'for' acts as a link.
(Other definitions for australia that I've seen before include "Film" , "Oz" , "USA lariat found down under" , "Test match players" , "Largest island in the world" .)