Caught milliner with case for windbag (10)
I believe the answer is:
chatterbox
'windbag' is the definition.
(thesaurus)
'caught milliner with case' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'milliner' becomes 'hatter' ('hatter' can be a synonym of 'milliner').
'with' means one lot of letters go next to another.
'case' becomes 'box' (boxing is a kind of casing).
'c'+'hatter'+'box'='CHATTERBOX'
'for' acts as a link.
(Other definitions for chatterbox that I've seen before include "Windbag" , "who goes on and on?" , "Babbler" , "talk show star, potentially?" , "One rabbiting on" .)