Slanderous attack (5)
I believe the answer is:
smear
'slanderous attack' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for smear that I've seen before include "Greasy/sticky mark" , "Badmouth" , "material for examination that is on the slide" , "Besmirch" , "False report" .)