A song from Maria Callas? (4)
I believe the answer is:
aria
'a song' is the definition.
(piece of music in an opera)
'from maria callas?' is the wordplay.
'from' says the answer is hidden in the clue.
'ARIA' is hidden in the letters of 'maria callas'.
(Other definitions for aria that I've seen before include "Operatic tune" , "Type of song" , "Operatic vocal" , "Repeated strain" , "Song such as "Your Tiny Hand is Frozen"" .)