Definitely not the very smallest (5,2,3)

'definitely' is the definition.
Both the answer and definition are adverbs. Perhaps you can see an association between them that I can't see?

'the very smallest' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'very' could be 'so' (both can mean 'extremely') and 'so' is found within the leftover letters.
This may be the basis of the clue (or it may be nonsense).

'not' is the link.

Can you help me to learn more?