melt vs unthaw

melt is a noun but unthaw is not a noun.

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

As verbs, melt and unthaw are synonyms defined as:

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

melt (noun)	unthaw (noun)
the process whereby heat changes something from a solid to a liquid

melt (verb)	unthaw (verb)
become or cause to become soft or liquid	become or cause to become soft or liquid
reduce or cause to be reduced from a solid to a liquid state, usually by heating
lose its distinct outline or shape; blend gradually
become more relaxed, easygoing, or genial
become less clearly visible or distinguishable; disappear gradually or seemingly
become less intense and fade away gradually