Part for diva is almost conventional (5)
I believe the answer is:
norma
'part for diva' is the definition.
(opera role which might be taken by a diva)
'almost conventional' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'conventional' becomes 'normal'.
'normal' with its final letter removed is 'NORMA'.
'is' is the link.
(Other definitions for norma that I've seen before include "Bellini work" , "Roman (anag) -- opera" , "The 'Rule' constellation" , "Bellini opera - girl's name" , "Girl's name - may be Roman" .)