Codswallop (6)
(Other definitions for piffle that I've seen before include "Twaddle" , "Balderdash" , "Stuff and nonsense" , "rot" , "Informal nonsense, worthless talk" .)
(Other definitions for bunkum that I've seen before include "Drivel" , "Ludicrously false statements" , "Slang nonsense, rubbish" , "Hogwash, rubbish" , "bombast" .)
'codswallop' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rot that I've seen before include "Decay or disintegrate" , "Decompose; rubbish" , "'Decay, decompose (3)'" , "Decay, perish" , "Drivel" .)
(Other definitions for tosh that I've seen before include "Rubbish, nonsense" , "Cobblers" , "Intimate" , "Stuff and nonsense" , "Drivel" .)