sky vs rainbow

sky and rainbow both are nouns.

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

sky (noun)	rainbow (noun)
the atmosphere and outer space as viewed from the earth	an illusory hope
	an arc of colored light in the sky caused by refraction of the sun's rays by rain

sky (verb)	rainbow (verb)
throw or toss with a light motion