overestimate vs estimation

overestimate and estimation both are nouns.

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

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

Other hypernyms of overestimate include approximation, estimate, idea.

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

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

Other hypernyms of overestimate include appraisal, estimate.

overestimate (noun)	estimation (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)

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