Opera beginning to look average (6)
I believe the answer is:
normal
'average' is the definition.
(I know that average can be written as normal)
'opera beginning to look' is the wordplay.
'opera' becomes 'norma' (Vincenzo Bellini opera).
'beginning to' suggests taking the first letters.
The initial letter of 'look' is 'l'.
'norma'+'l'='NORMAL'
(Other definitions for normal that I've seen before include "Usual, typical, expected" , "Usual - sane" , "Unremarkable" , "'Usual, typical (6)'" , "Ordinary, not extraordinary" .)