greenhouse gas UK /ˌɡɹiːn.haʊs ˈɡæs/US /ˌɡɹinˌ(h)aʊs ˈɡæs/ noun1 •Any gas (such as carbon dioxide, a chlorofluorocarbon (CFC), or methane) that contributes to the greenhouse effect when released into the atmosphere by absorbing infrared radiation emitted by a planet's surface, thus increasing the surface temperature.Termites and cows account for much greenhouse gas.Only two greenhouse gases get much attention. formsgreenhouse gases · greenhouse gasses