Melody, a flipping melody (4)
I believe the answer is:
aria
'melody' is the definition.
(I've seen this in another clue)
'melody a flipping' is the wordplay.
'melody' becomes 'air' (synonyms).
'flipping' is a reversal indicator.
'air'+'a'='aira'
'aira' in reverse letter order is 'ARIA'.
(Other definitions for aria that I've seen before include "Summertime perhaps" , "Vocal solo in a cantata etc" , "Refrain" , "Piece of music" , "Song from an opera (4)" .)