Chatting about trilby (3)
I believe the answer is:
hat
'trilby' is the definition.
(thesaurus)
'chatting about' is the wordplay.
'about' indicates the answer is hidden within the clue (the clue goes around or about the answer).
'HAT' is hidden in the letters of 'chatting'.
(Other definitions for hat that I've seen before include "Lid" , "One to cover head" , "opera?" , "Headdress" , "e.g. Pork pie" .)