Alien

Alien was a broad, subjective term. It could be applied as a noun or an adjective for any entity, object, place or practice which was not familiar. In one sense, it meant someone not from one's nation or locality. But more typically it was a synonym for extraterrestrials, or that which was "alien to humans". The Doctor, for instance, often admitted that they were an "alien" to their new human companions. (TV: Rose, The Runaway Bride, The Bells of Saint John, The Woman Who Fell to Earth)

However, the word was equally applicable to humans, from the perspective of extraterrestrials. As Melanie Bush once pointed out to an English cabbie suddenly brought in the presence of extraterrestrials, "We're all aliens to each other." (AUDIO: Unregenerate!) The Time Lords labelled Leela an alien when she visited Gallifrey. The Fourth Doctor, posing to fool the Vardans, ordered that she be banished from the Capitol for being alien. (TV: The Invasion of Time) Romana I once used the label "Earth alien" in reference to the natives of Earth. (TV: The Ribos Operation)

The term was trickier to apply to non-human Earth sapients. For instance, the Third Doctor referred to the Silurians as alien beings even after he discovered they had ruled the planet Earth millions of years before. (TV: Doctor Who and the Silurians) However, the Eleventh Doctor later stated that they were not aliens but rather "Earth...liens". (TV: The Hungry Earth)On an episode of Meet That Hero!, Supergirl introduced E.T. as "the sweetest alien ever". Later in the show, after E.T. grew a Kryptonian singing flower for her, she proposed the creation of an "alien club" - an idea the Twelfth Doctor was enthusiastic about, offering the help of his TARDIS. (WC: Supergirl Meets E.T.)

Revealing his true form to Ursula Blake and Elton Pope, "Victor Kennedy" proclaimed "You've dabbled with aliens... now meet the genuine article!" (TV: Love & Monsters)

When Major Jenny Maguire asked if it would be to insert misinformation onto the UNIT website as opposed to changing the passwords following the discovery that Mickey Smith was using www.whoisdoctorwho.co.uk to release sensitive information in 2006, Sergeant A. Frederick told her, scoldingingly, that she "[didn't have] time to knock up a load of fake conspiracy theories and fudged reports about aliens". (PROSE: Rose Tyler)

According to a joke book which the Doctor and Yaz became trapped within, the best alien at steering a car was a Drahvin. (PROSE: Knock! Knock! Who's There?)