Dictionary

protoplanet

noun pro·to·plan·et \ˈprō-tō-ˌpla-nət\

Definition of PROTOPLANET

:  a hypothetical whirling gaseous mass within a giant cloud of gas and dust that rotates around a sun and is believed to give rise to a planet
pro·to·plan·e·tary \ˌprō-tō-ˈpla-nə-ˌter-ē\ adjective

First Known Use of PROTOPLANET

1949

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