idea vs guesstimate

idea and guesstimate both are nouns.

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

As nouns, guesstimate is a hyponym of idea; that is, guesstimate is a word with a more specific, narrower meaning than idea:

idea (noun)	guesstimate (noun)
the content of cognition; the main thing you are thinking about	an estimate that combines reasoning with guessing
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

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