Note remaining briefly, musical symbol (4)
I believe the answer is:
clef
'musical symbol' is the definition.
(I've seen this in another clue)
'note remaining briefly' is the wordplay.
'note' becomes 'c' (musical note).
'remaining' becomes 'left' (synonyms).
'briefly' means to remove the last letter.
'left' with its last letter taken away is 'lef'.
'c'+'lef'='CLEF'
(Other definitions for clef that I've seen before include "that's marking the pitch" , "Staff note" , "Treble or bass on a stave" , "Symbol on the left of a musical stave" , "Musical key or stave" .)