Silently acting an operatic part is no good (6)

I believe the answer is:

miming

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'silently acting' is the definition.
'miming' can be an answer for 'acting' (thesaurus). I am not certain of the 'silently' bit.

'operatic part is no good' is the wordplay.
'operatic part' becomes 'mimi' (I can't explain this - if you can you should believe this answer much more).
'is no good' becomes 'ng' (abbreviation).
'mimi'+'ng'='MIMING'

'an' is the link.

Can you help me to learn more?

(Other definitions for miming that I've seen before include "Pretending to sing" , "Acting without words" .)

I've seen this clue in the Evening Standard.

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