The Collaborative International Dictionary of English v.0.48:

Besmirch \Be*smirch"\, v. t. [imp. & p. p. Besmirched; p. pr.
   & vb. n. Besmirching.]
   To smirch or soil; to discolor; to obscure. Hence: To
   dishonor; to sully. --Shak.
   [1913 Webster]