guestimate vs estimate

guestimate and estimate both are nouns.

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

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

Other hypernyms of guestimate include approximation, estimation, idea.

guestimate (noun)	estimate (noun)
an estimate that combines reasoning with guessing	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

guestimate (verb)	estimate (verb)
	judge tentatively or form an estimate of (quantities or time)
	judge to be probable