Frau von Trapp blows top in song (4)
I believe the answer is:
aria
'song' is the definition.
(piece of music in an opera)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for aria that I've seen before include "Opera solo" , "Air in an opera" , "Operatic air" , "Song such as "Your Tiny Hand is Frozen"" , "Operatic vocal" .)