Stress the melody (6)
I believe the answer is:
strain
I believe this is a double definition.
'stress' is the first definition.
(I know that stress can be written as strain)
'the melody' is the second definition.
(strain can mean a piece of music)
(Other definitions for strain that I've seen before include "Screen" , "Race" , "Distinct breed; use a seive" , "Pressure - filter" , "Blood" .)