The Collaborative International Dictionary of English v.0.48:

Denigration \Den`i*gra"tion\, n. [L. denigratio.]
   1. The act of making black. --Boyle.
      [1913 Webster]

   2. Fig.: A blackening; defamation.
      [1913 Webster]

            The vigorous denigration of science.  --Morley.
      [1913 Webster]

WordNet (r) 3.0 (2006):

denigration
    n 1: a belittling comment [syn: denigration, belittling]
    2: an abusive attack on a person's character or good name [syn:
       aspersion, calumny, slander, defamation,
       denigration]
    3: the act of expressing disapproval (especially of yourself)
       [syn: deprecation, denigration]