Make an effort on a tune (6)
I believe the answer is:
strain
I believe this clue is a double definition.
'make an effort' is the first definition.
(I've seen this before)
'tune' is the second definition.
(synonyms)
'on a' acts as a link.
(Other definitions for strain that I've seen before include "Filter - intense effort" , "line of ancestry" , "Pour through a sieve" , "Drain off" , "Family - tension" .)