[1] : The Collaborative International Dictionary of English v.0.48

slanderer \slan"derer\, n.
   one who slanders; a defamer; a calumniator. --jer. taylor.
   1913 webster

[2] : WordNet (r) 2.0

slanderer
     n : one who attacks the reputation of another by slander or
         libel syn: defamer, maligner, vilifier, libeler,
          backbiter, traducer
see also:
defamer maligner vilifier libeler backbiter traducer 

[3] : Moby Thesaurus II by Grady Ward, 1.0

22 moby thesaurus words for "slanderer":
   thersites, backbiter, belittler, calumniator, caustic critic,
   cynic, debunker, decrier, defamer, deflater, depreciator,
   derogator, detractor, disparager, hatchet man, knocker, libeler,
   muckraker, mudslinger, railer, social critic, traducer

[4] : Bouvier's Law Dictionary, Revised 6th Ed (1856)

slanderer. a calumniator, who maliciously and without reason imputes a crime 
or fault to another, of which he is innocent. 
     2. for this offence, when the slander is merely verbal, the remedy is 
an action on the case for damages; when it is reduced to writing or 
printing, it is a libel. q.v. 

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