underrating vs estimation

underrating and estimation both are nouns.

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

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

underrating: an estimation that is too low; an estimate that is less than the true or actual value
estimation: an approximate calculation of quantity or degree or worth

Other hypernyms of underrating include approximation, estimate, idea.

underrating (noun)	estimation (noun)
an estimation that is too low; an estimate that is less than the true or actual value	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)