superior planet vs major planet

superior planet and major planet both are nouns.

Word	Noun	Adjective	Verb	Adverb
superior planet	Yes	No	No	No
major planet	Yes	No	No	No

As nouns, major planet is a hypernym of superior planet; that is, major planet is a word with a broader meaning than superior planet:

superior planet: any of the planets whose orbit lies outside the earth's orbit
major planet: (astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction

Other hypernyms of superior planet include planet.

superior planet (noun)	major planet (noun)
any of the planets whose orbit lies outside the earth's orbit	(astronomy) any of the nine large celestial bodies in the solar system that revolve around the sun and shine by reflected light; Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto in order of their proximity to the sun; viewed from the constellation Hercules, all the planets rotate around the sun in a counterclockwise direction