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

I believe the answer is:

least of all

I'm a little stuck... Click here to teach me more about this clue!

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

I don't understand how the remainder of the clue works.

Can you help me to learn more?

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.