from Wiktionary, Creative Commons Attribution/Share-Alike License
- v. To not thaw; to (re-)freeze or remain frozen.
- v. To thaw out, to unfreeze; to become soft (of something which had been frozen).
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- v. become or cause to become soft or liquid
The senses, opposites in meaning, are from un- ("reverse, undo") + thaw ("melt") and un- ("release, extract") + thaw ("melt"), respectively. The sense "not thaw, remain frozen" is from the late 1500s. (Wiktionary)