Most unexcited about song (4)
I believe the answer is:
tune
'song' is the definition.
(I've seen this before)
'most unexcited about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'TUNE' can be found hidden inside 'most unexcited'.
(Other definitions for tune that I've seen before include "Adjust a radio receiver to a frequency" , "strain" , "Optimise the condition of" , "Song" , "temper" .)