guessing vs estimate

guessing and estimate both are nouns.

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

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

Other hypernyms of guessing include approximation, estimation, idea.

guessing (noun)	estimate (noun)
an estimate based on little or no information	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

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