At least one car's silent! (7)

I believe the answer is:

minimum

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'at least' is the definition.
'minimum' can be an answer for 'least' (I've seen this in another clue). I'm unsure of the 'at' bit.

'one car's silent' is the wordplay.
'one car' becomes 'mini' (Mini Cooper).
'silent' becomes 'mum' (keep mum).
'mini'+'mum'='MINIMUM'

Can you help me to learn more?

(Other definitions for minimum that I've seen before include "Least possible quantity" , "Lower limit" , "Lowest point" , "Least recorded value" , "Smallest possible quantity" .)

I've seen this clue in the Evening Standard.

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