The Collaborative International Dictionary of English v.0.48:

Defamation \Def`a*ma"tion\, n. [OE. diffamacioun, F.
   diffamation. See Defame.]
   Act of injuring another's reputation by any slanderous
   communication, written or oral; the wrong of maliciously
   injuring the good name of another; slander; detraction;
   calumny; aspersion.
   [1913 Webster]

   Note: In modern usage, written defamation bears the title of
         libel, and oral defamation that of slander. --Burrill.
         [1913 Webster]

WordNet (r) 3.0 (2006):

defamation
    n 1: a false accusation of an offense or a malicious
         misrepresentation of someone's words or actions [syn:
         defamation, calumny, calumniation, obloquy,
         traducement, hatchet job]
    2: an abusive attack on a person's character or good name [syn:
       aspersion, calumny, slander, defamation,
       denigration]