Help a character in opera (4)
I believe the answer is:
aida
'opera' is the definition.
(Aida is an opera by Giuseppe Verdi)
'help a character' is the wordplay.
'help' becomes 'aid' (synonyms).
'a character' becomes 'a'.
'aid'+'a'='AIDA'
'in' is the link.
(Other definitions for aida that I've seen before include "Verdi's opera set in ancient Egypt" , "title role" , "she dies entombed" , "Princess" , "Verdi opera" .)