Trivial conversation about milliner (7)
I believe the answer is:
chatter
'trivial conversation' is the definition.
(I've seen this before)
'about milliner' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa').
'milliner' becomes 'hatter' (synonyms).
'c'+'hatter'='CHATTER'
(Other definitions for chatter that I've seen before include "Insignificant talk" , "Prattle" , "Small talk" , "Gas" , "Talk rapidly" .)