Most large and silent (7)

I believe the answer is:

maximum

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'most' is the definition.
(thesaurus)

'large and silent' is the wordplay.
'large' becomes 'maxi' (I can't justify this - if you can you should believe this answer much more).
'and' is a charade indicator (letters next to each other).
'silent' becomes 'mum' (synonyms).
'maxi'+'mum'='MAXIMUM'

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(Other definitions for maximum that I've seen before include "Largest in group of numbers" , "The largest possible quantity or degree" , "Upper limit" , "Highest amount" , "Top" .)

I've seen this clue in the Evening Standard.

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