Note Mahler maybe failing to finish song (5)
I believe the answer is:
psalm
'song' is the definition.
(I've seen this before)
'note mahler maybe' is the wordplay.
'note' becomes 'ps' (PS is an example).
'mahler maybe' becomes 'alm' (I can't justify this - if you can you should believe this answer much more).
'ps'+'alm'='PSALM'
'failing to finish' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for psalm that I've seen before include "OT song" , "Old Testament lyrical poem or prayer" , "Sacred poem attributed to David" , "Jewish hymn" , "Song - hymn - prayer" .)