Smarter talk taking one in (7)
I believe the answer is:
'smarter' is the definition.
(natty can mean smart or stylish)
'talk taking one in' is the wordplay.
'talk' becomes 'natter' (I have seen 'Casual talk' mean 'natter' so perhaps 'talk' could also mean 'natter').
'taking one' becomes 'i' (Roman numeral. I am not sure about the 'taking' bit.).
'in' is an insertion indicator.
'natter' placed around 'i' is 'NATTIER'.
Can you help me to learn more?
(Other definitions for nattier that I've seen before include "Smarter and more fashionable" , "More clever" , "Like the smarter set" , "Louis XV court painter; more dapper" , "less scruffy" .)