periapsis vs periselene

periapsis and periselene both are nouns.

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

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

periapsis: (astronomy) the point in an orbit closest to the body being orbited
periselene: periapsis in orbit around the moon

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

periapsis (noun)	periselene (noun)
(astronomy) the point in an orbit closest to the body being orbited	periapsis in orbit around the moon