The Collaborative International Dictionary of English v.0.48:

Pollution \Pol*lu"tion\, n. [L. pollutio: cf. F. pollution.]
   1. The act of polluting, or the state of being polluted (in
      any sense of the verb); defilement; uncleanness; impurity.
      [1913 Webster]

   2. (Med.) The emission of semen, or sperm, at other times
      than in sexual intercourse. --Dunglison.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pollution
    n 1: undesirable state of the natural environment being
         contaminated with harmful substances as a consequence of
         human activities
    2: the state of being polluted [syn: befoulment, defilement,
       pollution]
    3: the act of contaminating or polluting; including (either
       intentionally or accidentally) unwanted substances or factors
       [syn: contamination, pollution] [ant: decontamination]