From Longman Dictionary of Contemporary Englishfossil fuelˈfossil ˌfuel ●○○ noun [countable, uncountable] TPGa fuel such as coal or oil that is produced by the very gradual decaying of animals or plants over millions of years Environmentalists would like to see fossil fuels replaced by renewable energy sources.
Examples from the Corpus
fossil fuel• The Government was also strongly backing an international trading system for fossil fuel emissions.• An obvious and technically achievable alternative to fossil fuel combustion is nuclear fission. 