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]

Moby Thesaurus II by Grady Ward, 1.0:

101 Moby Thesaurus words for "pollution":
   abomination, abuse, abuse of office, adulteration, air, atrocity,
   bad, badness, bane, bastardizing, befouling, befoulment,
   besmirchment, blight, contamination, conversion,
   corrupt administration, corruption, crying evil, cutting, damage,
   debasement, defalcation, defilement, desecration, despoliation,
   destruction, detriment, dilution, dirtying, diversion, doctoring,
   embezzlement, envenoming, evil, festering, fortifying, fouling,
   grievance, harm, harmfulness, havoc, health hazard, hurt, ill,
   infection, injuriousness, injury, insalubriousness, insalubrity,
   lacing, maladministration, malfeasance, malpractice, malversation,
   menace to health, misapplication, misappropriation, mischief,
   misconduct, misemployment, misfeasance, mishandling, mismanagement,
   misusage, misuse, noise pollution, noisomeness, noxiousness,
   outrage, pathenogenicity, peculation, perversion, pilfering,
   poison, poisoning, poor stewardship, profanation, prostitution,
   ritual uncleanness, soiling, spiking, spoiling, staining, sullying,
   suppuration, tainting, the worst, toxin, unhealthfulness,
   unhealthiness, unsalutariness, unwholesomeness, venom, vexation,
   violation, vitiation, water, watering, woe, wrong