mega-Earth

noun

A type of terrestrial planet, with masses greater than that of super-Earths. A dense planetary mass object with a solid surface and little atmosphere. An exoplanet with a mass comparable to a gas giant or ice giant, but without its massive gaseous envelope. A planet with a radius of 2 Earth radii or more, and a density of 5 g/cm³ or more.

OriginEnglish Earth ← Ancient Greek μέγᾰς (mégăs) ← Proto-Hellenic *mégas →
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Meanings

nounmega-Earth (plural mega-Earths)

plural mega-Earths

  1. astronomyA type of terrestrial planet, with masses greater than that of super-Earths. A dense planetary mass object with a solid surface and little atmosphere. An exoplanet with a mass comparable to a gas giant or ice giant, but without its massive gaseous envelope. A planet with a radius of 2 Earth radii or more, and a density of 5 g/cm³ or more.
    1. astronomyA post-Cthonian planet, whose gaseous envelope has completely or almost completely been stripped.

Origin

  1. Proto-Indo-European*méǵh₂s
  2. Proto-Hellenic*mégas
  3. Ancient Greekμέγᾰς (mégăs)
  4. Englishmega-
  5. EnglishEarth
  6. Englishmega-Earth

mega- + Earth. Treating "mega" as greater than "super". Named in relation to the term super-Earth.

Full word history & related roots →
Cite this entry
APA

mega-Earth. (n.d.). In WatkinsX Dictionary. Retrieved November 2, 2026, from https://dictionary.watkinsx.com/word/mega-Earth

MLA

“mega-Earth.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/mega-Earth. Accessed November 2, 2026.

Chicago

WatkinsX Dictionary, s.v. “mega-Earth,” accessed November 2, 2026, https://dictionary.watkinsx.com/word/mega-Earth.

Source: mega-Earth on Wiktionary, CC BY-SA 4.0.