alien

adjective

ˈā-lē-ən 

ˈāl-yən

1

a

: belonging or relating to another person, place, or thing : strange

an alien environment

b

: relating, belonging, or owing allegiance to another country or government : foreign

alien residents

c

: exotic sense 1

alien plants

d

: coming from another world : extraterrestrial

alien beings

an alien spaceship

When it comes to knowing what alien life forms might be like, we don't have any idea.

—Kate Shuster

2

: differing in nature or character typically to the point of incompatibility

ideas alien to democracy

alienly adverb

alienness

ˈā-lē-ən-nəs 

ˈāl-yən-nəs

noun

Synonyms of alien

• foreign

Choose the Right Synonym for alien

extrinsic, extraneous, foreign, alien mean external to a thing, its essential nature, or its original character.

extrinsic applies to what is distinctly outside the thing in question or is not contained in or derived from its essential nature.

sentimental value that is extrinsic to the house's market value

extraneous applies to what is on or comes from the outside and may or may not be capable of becoming an essential part.

arguments extraneous to the issue

foreign applies to what is so different as to be rejected or repelled or to be incapable of becoming assimilated.

techniques foreign to French cuisine

alien is stronger than foreign in suggesting opposition, repugnance, or irreconcilability.

a practice totally alien to her nature

Examples of alien in a Sentence

they were careful to learn of any alien business customs before trying to expand overseas

it's completely alien to her nature to wish evil of anyone

Recent Examples on the Web

This is because the main enemies in this game look to be large chitinous alien monsters, which your titular Gundam can slice into tiny pieces. —Ollie Barder, Forbes.com, 6 June 2026

The San Antonio Spurs' alien-like phenom scored just seven points in the first 24 minutes of Game 2 of the NBA Finals. —Ryan Morik, FOXNews.com, 6 June 2026

Steven Spielberg's upcoming return to the alien sci-fi genre, Disclosure Day, and last year's bombshell documentary, The Age of Disclosure. —Mike Miller, Entertainment Weekly, 5 June 2026

Or perhaps the brightening was caused by a free-floating planet (FFP) somewhere in our galaxy, a world ejected from an alien planetary system that could create a PBH-mimicking microlensing event of its own. —Jonathan O'Callaghan, Scientific American, 4 June 2026

Word History

Etymology

Middle English, "foreign," borrowed from Anglo-French, borrowed from Latin aliēnus "not one's own, of others, foreign, strange," derivative of alius "other" (perhaps going back to *aliai-nos, from an adverbialized locative derivative *aliai "elsewhere") — more at else entry 1

First Known Use

14th century, in the meaning defined at sense 1a

Phrases Containing alien

• anti-alien
• nonresident alien

Rhymes for alien

• episcopalian
• mammalian

Kids Definition

alien

1 of 2 adjective

ˈā-lē-ən 

ˈāl-yən

1

: relating or belonging to another country : foreign

alien residents

2

: exotic sense 1

3

: wholly different in nature or character

opinions alien to his outlook

4

: belonging or relating to another person, place, or thing : strange

5

: coming from another world : extraterrestrial

alien

2 of 2 noun

1

: a resident who was born elsewhere and is not a citizen of the country in which he or she now lives

2

: a being that comes from or lives in another world : extraterrestrial

3

: exotic

Legal Definition

alien

1 of 3 adjective

ˈā-lē-ən, ˈāl-yən 

: relating, belonging, or owing allegiance to another country or government

alien

2 of 3 noun

: a foreign-born resident who has not been naturalized and is still a subject or citizen of a foreign country

illegal aliens

an alien lawfully admitted to the United States for permanent residence

—U.S. Code

alien

3 of 3 transitive verb

: alienate

Etymology

Latin alienus not one's own, foreign