Loud elf used to be cheerless (7)
I believe the answer is:
doleful
'cheerless' is the definition.
(I've seen this before)
'loud elf used' is the wordplay.
'used' indicates an anagram.
'loud'+'elf'='loudelf'
'loudelf' is an anagram of 'DOLEFUL'.
'to be' is the link.
(Other definitions for doleful that I've seen before include "Mournful" , "down in the dumps" , "Miserable" , "Lugubrious" , "Melancholic" .)