unthaw

[Mark A. Mandel]

The prefix un- doesn't just mean 'negative'.  It also has a meaning of
'release'. From OED online:
un-, prefix[2]
expressing reversal or deprivation
sense [...] of freeing or releasing from something.

I don't have the reference at hand, but I'm pretty sure Whorf wrote about
this use as in "unravel" = "ravel" and several other examples that I can't
recall.

-- Mark A. Mandel
[This text prepared with Dragon NaturallySpeaking.]