Merriam-Webster Logo
SINCE 1828
Menu
×

An Encyclopædia Britannica Company

UFO

noun \ ˌyü-(ˌ)ef-ˈō \
See What's Trending Now See More Trending Words

Definition of UFO

plural UFO's or UFOs play \ˌyü-(ˌ)ef-ˈōz\
: an unidentified flying object; especially : flying saucer

See UFO defined for English-language learners

See UFO defined for kids

Origin and Etymology of ufo

unidentified flying object

UFO Defined for English Language Learners

UFO

noun

Definition of UFO for English Language Learners

  • : a flying object in the sky that some people believe could be a spaceship from another planet

Learn More about ufo

  1. See words that rhyme with UFO Spanish Central: Translation of UFO Nglish: Translation of UFO for Spanish speakers Britannica English: Translation of UFO for Arabic speakers

Seen and Heard

What made you want to look up UFO? Please tell us where you read or heard it (including the quote, if possible).

show hide

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

raillery

play

good-natured ridicule

Get Word of the Day daily email!

TRENDING NOW

  1. embolization 'the process by which a blood vessel or organ is obstructed by a material mass'

  2. oleaginous 'marked by an offensively ingratiating manner or quality'

  3. pansexual 'sexual desire or attraction...not limited to a particular gender identity or sexual orientation'

  4. symbiote 'an organism living in symbiosis'

  5. charlatan 'faker or fraud'

SEE ALL

BROWSE DICTIONARY

Ufa
UFO

Test Your Vocabulary

Words Used by Nabokov Quiz

  • image1676440788
  • Choose the best definition or synonym for the word in bold: "There are some eructations that sound like cheers—at least, mine did." Lolita
Spell It

Can you spell these 10 commonly misspelled words?

TAKE THE QUIZ
Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

Words at Play

alt-5b032d1aef0e9
'Ingenious' and 'Ingenuous': More Than a Typo

One's clever, the other's like a child

alt-5b0310daaafde
A Matter-of-Fact Look at 'Deadpan'

Surely we can be serious.

image1481409085
9 Words from the Magical Realm

When language is magic

alt-5afefa13cc811
A Field Guide to British Noble Titles

Know your Duchess from your Baroness

Ask the Editors

video-ghost-words
Ghost Word

The story of an imaginary word that managed to sneak past our editors and enter the dictionary.

image1760257654
2017 Word of the Year: Behind the Scenes

How we chose 'feminism'

video-literally
Literally

How to use a word that (literally) drives some people nuts.

video-his-or-her
Is Singular 'They' a Better Choice?

The awkward case of 'his or her'

Word Games

image1676440788
Words Used by Nabokov Quiz

How familiar are you with Nabokov’s unfamiliar vocabulary?

Take the quiz
cow-coming-home
Farm Idioms Quiz

Not your children's farm quiz.

Take the quiz
Spell It
Spell It

Can you spell these 10 commonly misspelled words?

Take the quiz
Word Winder's CrossWinder
Word Winder's CrossWinder

A game of winding words.

Play the game