Ninth Dimension
From Tardis Wiki, the free Doctor Who reference
The Ninth Dimension was a reality filled with many stars and planets. The Second Doctor sent the Arcturians' fleet of spaceships into the Ninth Dimension so they could find a planet on which to settle instead of Earth, as he knew that the people of Earth would most likely exterminate them. (PROSE: Only a Matter of Time)
The Twelfth Doctor mentions "battling Insects from the Ninth Dimension" to River Song as something that The Doctor might be busy doing. (TV: The Husbands of River Song)
