noun.
One who slanders or defames the name or reputation of another person.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
one who attacks the reputation of another by slander or libel
Word Usage
"A slanderer is one whose tongue is set on fire of hell; so much, and so directly, do these do the devil's work, that for it the devil's name is given to such."