guestimate vs estimation

guestimate and estimation both are nouns.

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

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

Other hypernyms of guestimate include approximation, estimate, idea.

guestimate (noun)	estimation (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)