Talk about Panama perhaps (4)
I believe the answer is:
chat
'talk' is the definition.
(thesaurus)
'about panama perhaps' is the wordplay.
'about' becomes 'c' (abbreviation for 'circa').
'panama perhaps' becomes 'hat' (panama is a kind of hat).
'c'+'hat'='CHAT'
(Other definitions for chat that I've seen before include "Small songbird of the thrush family" , "Friendly talk" , "Talking" , "Talk amiably - bird" , "An inconsequential and informal talk" .)