Talk smack about (5)
I believe the answer is:
trash
'talk smack about' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for trash that I've seen before include "Junk" , "Refuse; destroy" , "Worthless material to be disposed of" , "Wreck; rubbish" , "Garbage or nonsense" .)