guess vs estimate

guess and estimate both are nouns.

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

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

Other hypernyms of guess include approximation, estimation, idea.

As verbs, guess and estimate are synonyms defined as:

guess and estimate: judge tentatively or form an estimate of (quantities or time)

Other synonyms of guess include approximate, gauge, judge.

guess (noun)	estimate (noun)
an estimate based on little or no information	a judgment of the qualities of something or somebody
a message expressing an opinion based on incomplete evidence	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

guess (verb)	estimate (verb)
expect, believe, or suppose	judge tentatively or form an estimate of (quantities or time)
judge tentatively or form an estimate of (quantities or time)	judge to be probable
guess correctly; solve by guessing
put forward, of a guess, in spite of possible refutation