periapsis vs perigee

periapsis and perigee both are nouns.

Word	Noun	Adjective	Verb	Adverb
periapsis	Yes	No	No	No
perigee	Yes	No	No	No

As nouns, perigee is a hyponym of periapsis; that is, perigee is a word with a more specific, narrower meaning than periapsis:

periapsis: (astronomy) the point in an orbit closest to the body being orbited
perigee: periapsis in Earth orbit; the point in its orbit where a satellite is nearest to the Earth

Other hyponyms of periapsis include perihelion, perijove, perilune, periselene.

periapsis (noun)	perigee (noun)
(astronomy) the point in an orbit closest to the body being orbited	periapsis in Earth orbit; the point in its orbit where a satellite is nearest to the Earth