protoplanet
/ˈproʊtoʊˌplænɪt/
noun
- A large body of matter in space that is in the early stages of forming into a planet, before it becomes a fully developed planet.
- Over millions of years, the protoplanet grew large enough to become a rocky world.
- Astronomers observed a protoplanet forming in a distant star system.
- The young protoplanet was still gathering dust and gas from the surrounding disk.