permafrostPronunciation: /ˈpəːməfrɒst/Definition of permafrost noun [mass noun] a thick subsurface layer of soil that remains below freezing point throughout the year, occurring chiefly in polar regions: hilly terrain underlain by permafrostOrigin: 1940s: from permanent + frostpermafrost in other Oxford dictionaries Definition of permafrost in the US English dictionary
