from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Permanently frozen subsoil, occurring throughout the Polar Regions and locally in perennially frigid areas.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Permanently frozen ground, or a specific layer thereof.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. ground that is permanently frozen
perma(nent) + frost.(American Heritage® Dictionary of the English Language, Fourth Edition)
perma- + frost (Wiktionary)