SINCE 1828

An Encyclopædia Britannica Company

unheard-of

adjective un·heard-of \ ˌən-ˈhərd-ˌəv , -ˌäv \

Definition of unheard-of

:previously unknown; especially :unprecedented

moving at unheard-of speeds

See unheard-of defined for English-language learners

See unheard-of defined for kids

First Known Use of unheard-of

1592

unheard-of Synonyms

Synonyms

fresh, novel, original, strange, unaccustomed, unfamiliar, unheard-of, unknown, unprecedented

Antonyms

familiar, hackneyed, old, time-honored, tired, warmed-over

Related Words

innovative, unique; nontraditional, unconventional, untried, unused, unworn; pathbreaking, pioneering, trailblazing

Near Antonyms

conventional, established, traditional, tried, tried-and-true; derivative, imitative

UNHEARD-OF Defined for English Language Learners

unheard-of

adjective

Definition of unheard-of for English Language Learners

: not known to have existed or happened before : very unusual

UNHEARD-OF Defined for Kids

unheard-of

adjective un·heard-of \ ˌən-ˈhərd-ˌəv , -ˌäv \

Definition of unheard-of for Students

:not known before an unheard-of invention

Learn More about unheard-of

See words that rhyme with unheard-of Thesaurus: All synonyms and antonyms for unheard-of Nglish: Translation of unheard-of for Spanish speakers

Seen and Heard

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

show

WORD OF THE DAY

knee-jerk

play

readily predictable

BROWSE DICTIONARY

Test Your Vocabulary

The Exceptions Quiz III

Which of these words does not mean "nonsense"?

How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

TAKE THE QUIZ

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

TAKE THE QUIZ

Words at Play

alt-59e900afadac6

The Synonyms 'Discover' and 'Invent'

In the past, you could invent fruit.

alt-59e8c3440f453

I'll Have the Us(ual)

Shortening 'usual': easy to say, hard to spell

alt-59e77dc36c593

The Origins of 'Lobbyist'

From the front hallways to the back rooms

alt-59e673567065d

The History of the Word 'Terrorism'

Noah Webster first entered the term in 1840

Ask the Editors

video-title-words-of-the-year-1066

Words of the Year: 1066

Or, Why Pig Meat is Called 'Pork' and Cow Meat is Called 'Beef'

How Often Is 'Biweekly'?

Don't get us started on 'bimonthly'

video-irregardless-grammar-peeve-blend-of-the-synonyms-irrespective-and-regardless

Irregardless

It is in fact a real word (but that doesn't mean you should use it).

video-moose-goose-weird-plurals

Weird Plurals

One goose, two geese. One moose, two... moose. What's up with that?

Word Games

one-green-toy-robot-amidst-many-red-toy-robots

The Exceptions Quiz III

Which of these things doesn't belong?

Take the quiz

knupfer-painting-solon-before-croesus

Forms of Government Quiz

Name that government! Or something like that.

Take the quiz

How Strong Is Your Vocabulary?

How Strong Is Your Vocabulary?

Test your vocabulary with our 10-question quiz!

Take the quiz

Citation

Do you know the person or title these quotes describe?

Play the game