thaw vs unthaw

thaw is a noun but unthaw is not a noun.

Word	Noun	Adjective	Verb	Adverb
thaw	Yes	No	Yes	No
unthaw	No	No	Yes	No

As verbs, thaw and unthaw are synonyms defined as:

Other synonyms of thaw include dethaw, dissolve, melt, unfreeze.

thaw (noun)	unthaw (noun)
a relaxation or slackening of tensions or reserve; becoming less hostile
warm weather following a freeze; snow and ice melt
the process whereby heat changes something from a solid to a liquid

thaw (verb)	unthaw (verb)
become or cause to become soft or liquid	become or cause to become soft or liquid