Note tremolo after passing note (14)
I believe the answer is:
demisemiquaver
'note' is the definition.
(demisemiquaver is a kind of note)
'note tremolo after passing' is the wordplay.
'note' becomes 'mi' (as in 'do re mi').
'tremolo' becomes 'quaver' (tremolo is a quavering vocal effect).
'after' means one lot of letters go next to another.
'passing' becomes 'demise' (I've seen this before).
'mi'+'quaver'='miquaver'
'miquaver' put after 'demise' is 'DEMISEMIQUAVER'.
(Another definition for demisemiquaver that I've seen is " making very little sound".)