Make regular opera with pronounced deceit (9)
I believe the answer is:
normalise
'make regular' is the definition.
Both the definition and answer are verbs in their base form.
Maybe there's a link between them I don't understand?
'opera with pronounced deceit' is the wordplay.
'opera' becomes 'norma' (Vincenzo Bellini opera).
'with pronounced deceit' becomes 'lise' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'norma'+'lise'='NORMALISE'
Can you help me to learn more?
(Other definitions for normalise that I've seen before include "become commonplace" , "Standardise" , "Make usual" , "bring within limits" .)