look up any word, like half chub:
 
2.
a planet that scientists hypothesize is found beyond pluto. we cannot see it due to our meek scientific technology. there are cosmic radiation signals or something being emitted that make other planets orbit right or something like that that pluto cannot cause, so therefore there must be another planet doing it.
"we will one day find planet x"- some scientist.
by thegreatmonkey February 14, 2005
 
1.
A mystical planet that is apparently supposed to crash into earth on December 21st, 2012. Although there is no proof, people are still scared shitless because of this.
Planet X: IM COMING FOR U EARTH!
Brasil: NUU men plis attack europe!
Europe: TALLEY HO! ATTACK MEXICO!
Mexico: Si?
by TacoMann May 25, 2009