Engine

The Eleventh Doctor found that Starship UK was using a star whale in place of an engine. (TV: The Beast Below)

By one account, the Celestial Omnibus had an engine. (PROSE: Iris Wildthyme and the Unholy Ghost)

During the 21st century Dalek invasion, when the Tenth Doctor was at the Shadow Proclamation's headquarters, he noted that all the stolen planets fit together "like pieces of an engine". (TV: The Stolen Earth)