The term "island universe", or sometimes simply "universe", was sometimes applied as a synonym for "galaxy". In an interaction with Fomal, the First Doctor explained that his Tardis crossed the void between island universes, that he was from the Milky Way galaxy, and that Fomal's universe was the Crab Nebula, mentioning that his planet was the "Nebula of the Crab." (PROSE: The Sons of the Crab)
The Krotons mentioned returning from the planet of the Gonds back to their own "cosmos." (TV: The Krotons)
The Second Doctor once mused to Victoria Waterfield that if the Daleks succeeding in taking over Earth using the Dalek factor that he could try taking them to another universe. (TV: The Evil of the Daleks)
In 4000, Trantis believed the Tenth Galaxy was the largest of the Outer Galaxies because his empire spanned almost 20 solar systems, believing a "solar system" to be a star and its surrounding planets and other stars and their surrounding planets. When Sentreal explained that a galaxy held billions of solar systems, Trantis called this "the universe. (PROSE: Sentreal)