- any of the four planets with orbits outside the orbit of Mars, namely, the planets Jupiter, Saturn, Uranus, and Neptune.
Compare inner planet.
Origin of outer planet
First recorded in 1940–45
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018
Examples from the Web for outer planet
I've heard of it, but as this is my first outer-planet voyage, I know nothing about it.The Sargasso of Space
- any of the planets Jupiter, Saturn, Uranus, Neptune, and (formerly) Pluto, whose orbit lies outside the asteroid belt
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