overappraisal vs estimation

overappraisal and estimation both are nouns.

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

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

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

Other hypernyms of overappraisal include appraisal, estimate.

overappraisal (noun)	estimation (noun)
an appraisal that is too high	a judgment of the qualities of something or somebody
	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)