Song from Avatar I appreciated (4)
I believe the answer is:
aria
'song' is the definition.
(aria is a kind of song)
'from avatar i appreciated' is the wordplay.
'from' indicates the answer is hidden within the clue.
'ARIA' can be found hidden inside 'avatar i appreciated'.
(Other definitions for aria that I've seen before include "complex song" , "Musical performance" , "part of opera, maybe" , "Operatic vocal" , "Vocal solo in a cantata etc" .)