guesstimate vs guess

guesstimate and guess both are nouns.

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

As verbs, guess is a hypernym of guesstimate; that is, guess is a word with a broader meaning than guesstimate:

Other hypernyms of guesstimate include approximate, estimate, gauge, judge.

guesstimate (noun)	guess (noun)
an estimate that combines reasoning with guessing	an estimate based on little or no information
	a message expressing an opinion based on incomplete evidence

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