frostline

[ frawst-lahyn, frost- ]
/ ˈfrɔstˌlaɪn, ˈfrɒst- /

noun

the maximum depth at which soil is frozen.
the lower limit of permafrost.

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Origin of frostline

An Americanism dating back to 1860–65; frost + line1
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2020

British Dictionary definitions for frostline

frost line

noun

the deepest point in the ground to which frost will penetrate
the limit towards the equator beyond which frosts do not occur
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for frostline

frost line

In regions where there is no permafrost, the maximum depth to which frost penetrates the ground in the winter.
The lower limit of permafrost.
In tropical regions, the elevation below which frost never occurs.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.