Outcast discovered song (4)
I believe the answer is:
aria
'song' is the definition.
(aria is a kind of song)
'outcast discovered' is the wordplay.
'outcast' becomes 'pariah' (synonyms).
'discovered' means to look at the middle letters (dis-covered - outer letters removed).
The middle letters of 'pariah' are 'ARIA'.
(Other definitions for aria that I've seen before include "Imitative art work" , "Operatic part" , "Summertime perhaps" , "Operatic solo performance" , "Operatic air" .)