rainbow vs arc

rainbow and arc both are nouns.

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

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

rainbow: an arc of colored light in the sky caused by refraction of the sun's rays by rain
arc: something curved in shape

Other hypernyms of rainbow include bow.

rainbow (noun)	arc (noun)
an illusory hope	electrical conduction through a gas in an applied electric field
an arc of colored light in the sky caused by refraction of the sun's rays by rain	a continuous portion of a circle
	something curved in shape

rainbow (verb)	arc (verb)
	form an arch or curve