Crossword clues for the word: PLANETX The word PLANETX has appeared as an answer to at least 3 crossword clues on different crossword puzzles. Crossword clues for PLANETX Showing 1 to 3 of 3 results Clue(s) Hypothetical body in the solar system beyond Neptune Hypothetical solar system body beyond Neptune Term coined by Percival Lowell for a hypothetical world beyond Neptune