Before melody is heard (3)
I believe the answer is:
ere
'before' is the definition.
(usually literary)
'melody is heard' is the wordplay.
'melody' becomes 'air' ('air' can be a synonym of 'melody').
'is heard' indicates a 'sounds like' (homophone) clue.
'air' sounds like 'ERE'.
(Other definitions for ere that I've seen before include "Old word for before" , "Before (in poetry)" , "Before, poetically" , "Before (lit.)" , "Archaic word for before - a palindrome" .)