The Collaborative International Dictionary of English v.0.48:

Deprecation \Dep`re*ca"tion\ (d[e^]p`r[-e]*k[=a]"sh[u^]n), n.
   [L. deprecatio; cf. F. d['e]pr['e]cation.]
   1. The act of deprecating; a praying against evil; prayer
      that an evil may be removed or prevented. [archaic]
      [1913 Webster]

            Humble deprecation.                   --Milton.
      [1913 Webster]

   2. Entreaty for pardon; petitioning.
      [1913 Webster]

   3. An imprecation or curse. [Obs.] --Gilpin.
      [1913 Webster]

   4. A strong expression of disapprobation; an expression of a
      low opinion.
      [PJC]

WordNet (r) 3.0 (2006):

deprecation
    n 1: a prayer to avert or remove some evil or disaster
    2: the act of expressing disapproval (especially of yourself)
       [syn: deprecation, denigration]