Source : Webster's Revised Unabridged Dictionary (1913)

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.

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

Source : WordNet®

defamation
     n 1: a malicious attack [syn: {calumny}, {obloquy}, {traducement},
           {hatchet job}]
     2: an abusive attack on a person's character or good name [syn:
         {aspersion}, {calumny}, {slander}, {denigration}]