What does alien mean?
The word alien has two principal meanings that share a common thread of 'otherness'. In its oldest and most formal sense, an alien is a person who belongs to a foreign country or nation — particularly one residing under the jurisdiction of a state whose citizenship they do not hold, as in immigration law's distinction between citizens and resident aliens. In its far more popular modern sense, an alien is a being from another planet, a meaning cemented by twentieth-century science fiction and now often the first association people make with the word. As an adjective, alien describes anything foreign, unfamiliar, or at odds with one's nature or interests — an alien concept, an alien environment, an alien culture. The word derives from the Latin alienus, meaning 'belonging to another', which also gives us alienate and alienation. Because it straddles law, science fiction, and everyday language, alien is a versatile term whose connotation ranges from neutral legal classification to eerie, hostile strangeness.
A person who belongs to a foreign country or nation; especially one residing in or owing allegiance to a different state. Also, in popular usage, a being from another planet.
"Under the new legislation, every alien working in the country must obtain a permit."
In legal contexts, 'alien' is increasingly replaced by 'foreign national'; in general usage, the extraterrestrial sense now dominates.
Belonging to another person, place, or thing; foreign, unfamiliar, or repugnant to one's nature, interests, or sympathies.
"The bureaucracy felt utterly alien to her free-spirited temperament."
Standard pluralization applies; used for both foreign nationals and extraterrestrial beings.
"The archive catalogued dozens of alleged sightings of aliens across the decade."
The word 'alien' comes from the Latin 'alienus' — literally 'belonging to someone else' — so every time you call something alien, you're using a word the ancient Romans used for other people's property.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of alien
Alien comes from the Latin adjective alienus, meaning 'belonging to another person or place', itself derived from alius ('other, another'). The word entered English via Old French in the medieval period, initially carrying legal weight: an 'alien' was a foreign-born person without citizenship rights. The related verb alienate and noun alienation come from the same Latin root, originally referring to the transfer of property away from its owner before extending to emotional estrangement. Cognates include allegiance (from the same feudal-legal tradition) and eligible/ineligible, which share the Latin root through Old French.
Related word forms
How alien is actually used
In formal legal contexts, 'alien' specifically denotes a non-citizen — though modern usage increasingly prefers terms like 'foreign national'. In everyday and popular culture, 'alien' overwhelmingly evokes extraterrestrial beings. As an adjective it can carry a negative connotation of strangeness or hostility ('alien concept', 'alien environment').
Easily confused with alien
Alienate is a verb meaning to cause someone to feel isolated or hostile, while alien as a noun refers to a foreigner or extraterrestrial being.
A foreigner is simply someone from another country, whereas alien carries legal (immigration) or science-fiction connotations beyond mere nationality.