Definition of planetesimal
: any of numerous small celestial bodies that may have existed at an early stage of the development of the solar system
Recent Examples of planetesimal from the Web
Dwarf planets have been defined by the International Astronomical Union since 2006 as celestial bodies that are roundish like their larger cousins in the solar system, but which haven’t gobbled up all the other planetesimals near themselves.
These example sentences are selected automatically from various online news sources to reflect current usage of the word 'planetesimal'. Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
Origin and Etymology of planetesimal
planet + -esimal (as in infinitesimal)
First Known Use: 1903See Words from the same year
Seen and Heard
What made you want to look up planetesimal? Please tell us where you read or heard it (including the quote, if possible).