Filter — melody (6)
I believe the answer is:
strain
This clue is a double definition.
'filter' is the first definition.
(I know that filter can be written as strain)
'melody' is the second definition.
(I know that melody can be written as strain)
(Other definitions for strain that I've seen before include "Weaken -- sieve" , "Strive; ancestry" , "Remove by passing through a filter" , "Pass through a colander" , "Family - stress - air - force" .)