Jovian planet vs major planet

Jovian planet and major planet both are nouns.

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

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

Jovian planet: any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature (like Jupiter)
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 Jovian planet include planet.

Jovian planet (noun)	major planet (noun)
any of the four outermost planets in the solar system; much larger than Earth and gaseous in nature (like Jupiter)	(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