idea vs overestimate

idea and overestimate both are nouns.

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

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

idea (noun)	overestimate (noun)
the content of cognition; the main thing you are thinking about	a calculation that results in an estimate that is too high
your intention; what you intend to do	an appraisal that is too high
an approximate calculation of quantity or degree or worth
a personal view
(music) melodic subject of a musical composition

idea (verb)	overestimate (verb)
	make too high an estimate of
	assign too high a value to