The least diminutive mother

I believe the answer is:

minimum

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'the least' is the definition.
(I've seen this before)

'diminutive mother' is the wordplay.
'diminutive' becomes 'mini' (I can't explain this - if you can you should believe this answer much more).
'mother' becomes 'mum' (informal term for mother).
'mini'+'mum'='MINIMUM'

Can you help me to learn more?

(Other definitions for minimum that I've seen before include "The least of smallest amount possible" , "Lowest point" , "Lowest value" , "Bottom" , "Least possible quantity" .)

I've seen this clue in the Irish Independent.

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