undervalue vs decrease

undervalue is not a noun while decrease is a noun.

Word	Noun	Adjective	Verb	Adverb
undervalue	No	No	Yes	No
decrease	Yes	No	Yes	No

As verbs, decrease is a hypernym of undervalue; that is, decrease is a word with a broader meaning than undervalue:

Other hypernyms of undervalue include diminish, fall, lessen.

undervalue (noun)	decrease (noun)
	the act of decreasing or reducing something
	the amount by which something decreases
	a change downward
	a process of becoming smaller or shorter

undervalue (verb)	decrease (verb)
lose in value	decrease in size, extent, or range
assign too low a value to	make become smaller
esteem lightly