Chat and a fag (6)
I believe the answer is:
gasper
'fag' is the definition.
(slang term for a cigarette)
'chat and a' is the wordplay.
'chat' becomes 'gas' (informal term meaning to chat).
'and' says to put letters next to each other.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'gas'+'per'='GASPER'
(Other definitions for gasper that I've seen before include "Pagers (anag) - cigarette (slang)" , "fag" , "Ciggie" , "Cigarette; one catching breath" , "Grapes (anag) -- cigarette (slang)" .)