perigee vs periapsis

perigee and periapsis both are nouns.

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

As nouns, periapsis is a hypernym of perigee; that is, periapsis is a word with a broader meaning than perigee:

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

Other hypernyms of perigee include point of periapsis.

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