From Longman Dictionary of Contemporary Englishacid rainˌacid ˈrain noun [uncountable] SGPrain that contains harmful acid which can damage the environment and is caused by chemicals in the air, for example from cars or factories
Examples from the Corpus
acid rain• There will be displays on acid rain, the ozone layer and global warming.• Ever tighter regulations are being introduced to protect the environment from emissions contributing to the greenhouse effect or acid rain.• It dismisses suggestions that acid rain is a key factor in declining tree health.• Better that Aretha Franklin had not been born than that we should endure a drop more of this acid rain of spittle!• Hydrocarbons also contribute both to acid rain and to ozone formation. 