Adeki was a planet.
History[]
The native species of Adeki were wiped out when the shape-shifting Gwanzulums became stranded on the planet and drained their life-force.
Some time later, while fishing on Adeki, the Seventh Doctor met what he thought were some of his prior companions: Adric, Sara Kingdom, Katarina, Jamie McCrimmon and Peri, as well as some of his previous incarnations. These visions each turned out to be Gwanzulums, who were stranded on Adeki and hoped to trick the Doctor into helping them leave. The Doctor realised this and escaped without taking any of them with him. (COMIC: Planet of the Dead)