Film critic on TV once snubbed opera (5)
I believe the answer is:
norma
'opera' is the definition.
(Vincenzo Bellini opera)
'film critic on tv once snubbed' is the wordplay.
'film critic on tv once' becomes 'Norman' (film critic Barry Norman).
'snubbed' means to remove the last letter (could historically mean cutting the end off).
'norman' with its last letter taken away is 'NORMA'.
(Other definitions for norma that I've seen before include "small group of stars" , "Operatic work" , "John Major's wife - Bellini opera" , "- - Jean Baker: Marilyn Monroe" , "Game; shared supply" .)