rainbow vs promise

rainbow and promise both are nouns.

Word	Noun	Adjective	Verb	Adverb
rainbow	Yes	No	No	No
promise	Yes	No	Yes	No

As nouns, promise is a hypernym of rainbow; that is, promise is a word with a broader meaning than rainbow:

Other hypernyms of rainbow include hope.

rainbow (noun)	promise (noun)
an illusory hope	grounds for feeling hopeful about the future
an arc of colored light in the sky caused by refraction of the sun's rays by rain	a verbal commitment by one person to another agreeing to do (or not to do) something in the future

rainbow (verb)	promise (verb)
	make a promise or commitment
	promise to undertake or give
	make a prediction about; tell in advance
	give grounds for expectations