overvalue vs overestimate

overvalue is not a noun while overestimate is a noun.

Word	Noun	Adjective	Verb	Adverb
overvalue	No	No	Yes	No
overestimate	Yes	No	Yes	No

As verbs, overvalue and overestimate are synonyms defined as:

overvalue (noun)	overestimate (noun)
	a calculation that results in an estimate that is too high
	an appraisal that is too high

overvalue (verb)	overestimate (verb)
assign too high a value to	make too high an estimate of
	assign too high a value to