before vowels ap-, word-forming element meaning "of, from, away from; separate, apart from, free from," from Greek apo "from, away from; after; in descent from," in compounds, "asunder, off; finishing, completing; back again," of time, "after," of origin, "sprung from, descended from; because of," from PIE root *apo- "off, away" (source also of Sanskrit apa "away from," Avestan apa "away from," Latin ab "away from, from," Gothic af, Old English of "away from," Modern English of, off).

Earth as a goddess, from Greek Gaia, spouse of Uranus, mother of the Titans, personification of gaia "earth" (as opposed to heaven), "land" (as opposed to sea), "a land, country, soil;" it is a collateral form of gē (Dorian ga) "earth," which is of unknown origin and perhaps from a pre-Indo-European language of Greece. The Roman equivalent goddess of the earth was Tellus (see tellurian), sometimes used in English poetically or rhetorically for "Earth personified" or "the Earth as a planet."

"point farthest from the sun" (of a celestial body's orbit), 1670s, a Grecianized form of Modern Latin aphelium (itself attested in English from 1650s), coined by Johannes Kepler based on Greek apo hēliou "away from the sun." The word is thus an assimilated form of apo "away from" (see apo-) + hēliou, genitive of hēlios "sun" (from PIE root *sawel- "the sun"), formed on the model of Ptolemaic apogaeum (see apogee) to reflect the new heliocentric model of the universe.

"point at which a celestial body is nearest the Earth," 1590s, from Modern Latin perigeum (15c.), from Late Greek peregeion, used by Ptolemy as a noun, properly neuter of adjective perigeios "near the earth," from peri ges, from peri "near" (see peri-) + ges, genitive of gē "earth" (see Gaia). Now only of the moon, formerly used also for the corresponding point in the orbit of any celestial body. Compare apogee.