Slander or libel (6)
I believe the answer is:
defame
I believe this clue is a double definition.
'slander' is the first definition.
(I know that slander can be written as defame)
'libel' is the second definition.
(I've seen this in another clue)
(Other definitions for defame that I've seen before include "Charge falsely" , "Damage (someone's) reputation" , "'Denigrate, slander (6)'" , "Injure the reputation of" , "Damage the reputation (of someone)" .)