guesstimate vs estimation

guesstimate and estimation both are nouns.

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

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

Other hypernyms of guesstimate include approximation, estimate, idea.

guesstimate (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)

guesstimate (verb)	estimation (verb)
estimate based on a calculation