overestimate vs estimate

overestimate and estimate both are nouns.

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

As nouns, estimate is a hypernym of overestimate; that is, estimate is a word with a broader meaning than overestimate:

Other hypernyms of overestimate include approximation, estimation, idea.

As nouns, estimate is a hypernym of overestimate; that is, estimate is a word with a broader meaning than overestimate:

overestimate: an appraisal that is too high
estimate: a document appraising the value of something (as for insurance or taxation)

Other hypernyms of overestimate include appraisal, estimation.

overestimate (noun)	estimate (noun)
a calculation that results in an estimate that is too high	a judgment of the qualities of something or somebody
an appraisal that is too high	an approximate calculation of quantity or degree or worth
	the respect with which a person is held
	a document appraising the value of something (as for insurance or taxation)
	a statement indicating the likely cost of some job

overestimate (verb)	estimate (verb)
make too high an estimate of	judge tentatively or form an estimate of (quantities or time)
assign too high a value to	judge to be probable