keynote vs idea

keynote and idea both are nouns.

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

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

Other hypernyms of keynote include thought.

keynote (noun)	idea (noun)
a fundamental or central idea	the content of cognition; the main thing you are thinking about
(music) the first note of a diatonic scale	your intention; what you intend to do
the principal theme in a speech or literary work	an approximate calculation of quantity or degree or worth
	a personal view
	(music) melodic subject of a musical composition

keynote (verb)	idea (verb)
set the keynote of
give the keynote address to (an audience)