idea vs sentiment

idea and sentiment both are nouns.

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

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

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

Other hypernyms of idea include opinion, persuasion, thought, view.

idea (noun)	sentiment (noun)
the content of cognition; the main thing you are thinking about	a personal belief or judgment that is not founded on proof or certainty
your intention; what you intend to do	tender, romantic, or nostalgic feeling or emotion
an approximate calculation of quantity or degree or worth
a personal view
(music) melodic subject of a musical composition