A smaller amount than any of the others? Certainly not! (5,2,3)

'a smaller' is the definition.
I can't judge whether this defines the answer.

'amount than any of the others? certainly not' is the wordplay.
I cannot quite understand how this works, but
'amount' could be 'least' (least is a kind of amount) and 'least' is found in the answer.
'any' could be 'all' (similar in meaning) and 'all' is found within the answer.
'of' could be 'o' and 'o' is found in the answer.
A single letter 'f' remains which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?