Douglas Harper's Etymology Dictionary
Wiktionary
unthaw
vb. 1 To not thaw; to (re-)freeze or remain frozen. 2 To thaw out, to unfreeze; to become soft (of something which had been frozen).
WordNet
Usage examples of "unthaw".
She was cold, but the heater in her Bronco would unthaw her hands and feet.
If he ever hoped to unthaw her, he knew he would have to go about it in a different way.
Going to the refrigerator, she pulled out two steaks she had set in it the night before to unthaw, eggs, canned biscuits and milk.
They stopped only to unthaw their hands and feet and warm a little tea.