Loud elf unusually sad (7)
I believe the answer is:
doleful
'sad' is the definition.
(I've seen this before)
'loud elf unusually' is the wordplay.
'unusually' is an anagram indicator.
'loud'+'elf'='loudelf'
'loudelf' is an anagram of 'DOLEFUL'.
(Other definitions for doleful that I've seen before include "Melancholic" , "not happy?" , "Sad" , "Cheerless" , "Dismal" .)