sentiment vs idea

sentiment and idea both are nouns.

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

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

sentiment: a personal belief or judgment that is not founded on proof or certainty
idea: a personal view

sentiment (noun)	idea (noun)
a personal belief or judgment that is not founded on proof or certainty	the content of cognition; the main thing you are thinking about
tender, romantic, or nostalgic feeling or emotion	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