Definition of protoplanet in English:

protoplanet

noun

Astronomy
  • A large body of matter in orbit around the sun or a star and thought to be developing into a planet.

    ‘this analysis supported the view that the moon originated from a glancing collision between the earth and another protoplanet 4,500 million years ago’
    • ‘Learning more about the protoplanet won't be fast or easy.’
    • ‘The protoplanet candidate orbits about 70 times further from its star than Earth does from the Sun.’
    • ‘There are indications that the surroundings of the protoplanet are potentially heated up by the formation process.’
    • ‘Many scientists think it's a protoplanet left over from the solar system's first few million years.’
    • ‘It isn't clear how the latest suspected protoplanet is being formed.’

Origin

1940s: from proto- + planet.

Pronunciation:

protoplanet

/ˈprəʊtəʊˌplanɪt/