The Collaborative International Dictionary of English v.0.48:

Dirty \Dirt"y\, v. t. [imp. & p. p. Dirtied; p. pr. & vb. n.
   Dirtying.]
   1. To foul; to make filthy; to soil; as, to dirty the clothes
      or hands.
      [1913 Webster]

   2. To tarnish; to sully; to scandalize; -- said of
      reputation, character, etc.
      [1913 Webster]