underestimate vs estimate

underestimate and estimate both are nouns.

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

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

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

Other hypernyms of underestimate include approximation, estimation, idea.

As verbs, estimate is a hypernym of underestimate; that is, estimate is a word with a broader meaning than underestimate:

Other hypernyms of underestimate include approximate, gauge, guess, judge.

underestimate (noun)	estimate (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)
	a statement indicating the likely cost of some job

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