Mum, able to listen (6)

I believe the answer is:

silent

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'mum' is the definition.
(to keep mum can informally mean to stay silent)

'able to listen' is the wordplay.
'listen' can be anagrammed to 'SILENT'.
Though, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for silent that I've seen before include "Making no noise" , "Not speaking" , "Listen in order to be quiet" , "Making no sound" , "Like William Prince of Orange" .)

I've seen this clue in the Evening Standard.

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