Harmful libel (6)
I believe the answer is:
malign
I believe this clue is a double definition.
'harmful' is the first definition.
(associated in meaning)
'libel' is the second definition.
(I've seen this in another clue)
(Other definitions for malign that I've seen before include "Laming, showing malice" , "Vilify, denigrate." , "Showing malice or great ill will" , "Showing malice, say harmful things about" , "Ill-disposed - defame" .)