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]

The Collaborative International Dictionary of English v.0.48:

dirtying \dirtying\ n.
   the act of soiling something.

   Syn: soiling, soilure.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

dirtying
    n 1: the act of soiling something [syn: soiling, soilure,
         dirtying]