UNTHAW

dissolve, thaw, unfreeze, unthaw, dethaw, melt

(verb) become or cause to become soft or liquid; “The sun melted the ice”; “the ice thawed”; “the ice cream melted”; “The heat melted the wax”; “The giant iceberg dissolved over the years during the global warming phase”; “dethaw the meat”

Source: WordNet® 3.1

Etymology

Verb

unthaw (third-person singular simple present unthaws, present participle unthawing, simple past and past participle unthawed)

(ambitransitive) To thaw out, to unfreeze; to become soft (of something which had been frozen).

Source: Wiktionary