whimsy vs idea

whimsy and idea both are nouns.

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

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

Other hypernyms of whimsy include thought.

whimsy (noun)	idea (noun)
the trait of acting unpredictably and more from whim or caprice than from reason or judgment	the content of cognition; the main thing you are thinking about
an odd or fanciful or capricious idea	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