planet vs heavenly body

planet and heavenly body both are nouns.

Word	Noun	Adjective	Verb	Adverb
planet	Yes	No	No	No
heavenly body	Yes	No	No	No

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

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
heavenly body: natural objects visible in the sky

Other hypernyms of planet include celestial body.

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

planet: any celestial body (other than comets or satellites) that revolves around a star
heavenly body: natural objects visible in the sky

Other hypernyms of planet include celestial body.

planet (noun)	heavenly body (noun)
(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	natural objects visible in the sky
any celestial body (other than comets or satellites) that revolves around a star
a person who follows or serves another