proposal vs suggestion

proposal and suggestion both are nouns.

Word	Noun	Adjective	Verb	Adverb
proposal	Yes	No	No	No
suggestion	Yes	No	No	No

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

proposal (noun)	suggestion (noun)
something proposed (such as a plan or assumption)	the act of inducing hypnosis
the act of making a proposal	an idea that is suggested
an offer of marriage	the sequential mental process in which one thought leads to another by association
	a proposal offered for acceptance or rejection
	persuasion formulated as a suggestion
	a just detectable amount