guesstimate vs idea

guesstimate and idea both are nouns.

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

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

Other hypernyms of guesstimate include approximation, estimate, estimation.

guesstimate (noun)	idea (noun)
an estimate that combines reasoning with guessing	the content of cognition; the main thing you are thinking about
	your intention; what you intend to do
	an approximate calculation of quantity or degree or worth
	a personal view
	(music) melodic subject of a musical composition

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