From Longman Dictionary of Contemporary Englishpermafrostper‧ma‧frost /ˈpɜːməfrɒst $ ˈpɜːrməfrɒːst/ noun [uncountable] HEGa layer of soil that is always frozen in countries where it is very cold
Examples from the Corpus
permafrost• Lenses of rather pure ice are conceivable, but more likely is a permafrost containing 10 percent to 30 percent ice.• Undulating coastal plains and other ungraded lowlands, underlain by permafrost, in summer form some of the tundra's wettest areas.• Water extraction from permafrost by distillation seems rather straight forward.• Very important to know, because suppose you got permafrost under your concrete slab?• Florence in permafrost Cold pinches the hills around Florence.• Most of Mars seems to be covered with a layer of permafrost, kilometers deep in places.• The first option is to extract water from subsurface permafrost and use that water directly in a nuclear or solar steam rocket.• Fulton lay on the permafrost, miming a cerebral haemorrhage.Origin permafrost (1900-2000) permanent + frost 