Crossword Genius

Extremes in formal use, not likely how a native speaks? (8)

Ross

I believe the answer is:

fluently

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

'extremes in' is the definition.
Both the answer and definition are adverbs. Maybe you can see a link between them that I don't see?

'formal use not likely how a native speaks?' is the wordplay.
I cannot really understand how this works, but
'not' could be 'nt' (synonyms) and 'nt' is present in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for fluently that I've seen is " smoothly spoken".)

I've seen this clue in The Times.
Want a hint initially instead of a full solution? Install my app