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frostline

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

noun

  1. the maximum depth at which soil is frozen.

  2. the lower limit of permafrost.

Etymology

Origin of frostline

An Americanism dating back to 1860–65; frost + line 1

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.