melody vs idea

melody and idea both are nouns.

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

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

melody (noun)	idea (noun)
the perception of pleasant arrangements of musical notes	the content of cognition; the main thing you are thinking about
a succession of notes forming a distinctive sequence	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