Held on to note on organ (5)
I believe the answer is:
clung
'held on' is the definition.
(I've seen this in another clue)
'note on organ' is the wordplay.
'note' becomes 'c' (musical note).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'organ' becomes 'lung' (lung is a kind of organ).
'c'+'lung'='CLUNG'
'to' acts as a link.
(Other definitions for clung that I've seen before include "Held on tight" , "Was emotionally close" , "Held on tightly" , "Held on desperately" .)