idea vs melodic line

idea and melodic line both are nouns.

Word	Noun	Adjective	Verb	Adverb
idea	Yes	No	No	No
melodic line	Yes	No	No	No

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

Other hypernyms of idea include air, line, melodic phrase, melody, strain, tune.

idea (noun)	melodic line (noun)
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