Unfortunate act ends melody (7)
I believe the answer is:
descant
'melody' is the definition.
(descant is a kind of melody)
'unfortunate act ends' is the wordplay.
'unfortunate' is an anagram indicator.
'act'+'ends'='actends'
'actends' with letters rearranged gives 'DESCANT'.
(Other definitions for descant that I've seen before include "Accompaniment added above a basic melody" , "Treble melody part" , "Independent treble line" , "Upper melody" , "Sung variation" .)