Finishes berating April and Adam over tendency to badmouth (6)
I believe the answer is:
malign
'to badmouth' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for malign that I've seen before include "run down" , "Traduce" , "Defame, vilify" , "Evil, baleful" , "Evil, malevolent" .)