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planet X

[ plan-it eks ]
/ ˈplæn ɪt ˈɛks /
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noun Astronomy.
a planet beyond the orbit of Pluto whose existence has been hypothesized but not confirmed.
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Origin of planet X

First recorded in 1880–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022

How to use planet X in a sentence

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