1. The introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of chemical substances or energy, such as noise, heat or light. Pollutants, the components of pollution, can be either foreign substances/energies or naturally occurring contaminants. Pollution is often classed as point source or nonpoint source pollution. (wikipedia.org)
2. The change in the environment caused by natural or artificial input of harmful contaminants into the environment, and may cause instability, disruption or harmful effects to the ecosystem. (biology-online.org)
3. The act of polluting; the state of being polluted. (biology-online.org)
4. The pollutant or contaminant in the environment. (biology-online.org)
5. The action of polluting especially by environmental contamination with man-made waste; also, the condition of being polluted (merriam-webster.com); undesirable state of the natural environment being contaminated with harmful substances as a consequence of human activities (wordnetweb.princeton.edu).
6. The addition of any substance (solid, liquid, or gas) or any form of energy (such as heat, sound, or radioactivity) to the environment at a rate faster than it can be dispersed, diluted, decomposed, recycled, or stored in some harmless form. (global.britannica.com)
Word origin: From Late Latin pollutionem (nominative pollutio) “defilement,” noun of action from past participle stem of Latin polluere “to soil, defile, contaminate,” from por– “before” + –luere “smear,”