| precipitation, as rain, snow, or sleet, containing relatively high concentrations of acid-forming chemicals, as the pollutants from coal smoke, chemical manufacturing, and smelting, that have been released into the atmosphere and combined with water vapor: harmful to the environment. |
| acid rain n. Acid precipitation falling as rain. |
A type of precipitation made up of dilute acids, primarily a by-product of heavy industry.
Note: Acid rain is a result of the combination of water with chemicals released into the atmosphere by the burning of fossil fuels.