Roman composition, an opera (5)
I believe the answer is:
norma
'opera' is the definition.
(I've seen this in another clue)
'roman composition' is the wordplay.
'composition' indicates anagramming the letters (letters arranged or composed in a different order).
'roman' with letters rearranged gives 'NORMA'.
'an' is the link.
(Other definitions for norma that I've seen before include "Bellini work" , "Outdoor function" , "Operatic heroine" , "Roman (anag) -- opera" , "Bellini drama" .)