Song belter, possibly? (6)
I believe the answer is:
treble
'song' is the definition.
(thesaurus)
'belter possibly?' is the wordplay.
'possibly?' is an anagram indicator (I've seen 'possibly' mean this).
'belter' anagrammed gives 'TREBLE'.
(Other definitions for treble that I've seen before include "High-frequency (radio control knob)" , "High voice - large drink" , "Boy chorister" , "Three times as many" , "Make or become three times as much" .)