Marilyn, originally (5)
I believe the answer is:
norma
'marilyn originally' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for norma that I've seen before include "Roman (anag) -- opera" , "Marilyn was properly one" , "musical work" , "Bellini heroine" , "Bellini's heroine" .)