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

libeler \li"beler\ -~er, n.
   one who libels. written also libeller. " libelers of
   others." --buckminster.
   1913 webster
see also:
libeller 

[2] : WordNet (r) 2.0

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

Libeler >> L Words
Libeler, definition of term: Libeler
libeler_pag1.html