merge vs melt

merge is not a noun while melt is a noun.

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

As verbs, melt is a hyponym of merge; that is, melt is a word with a more specific, narrower meaning than merge:

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

merge (verb)	melt (verb)
become one	become or cause to become soft or liquid
mix together different elements	reduce or cause to be reduced from a solid to a liquid state, usually by heating
join or combine	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