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• unheard-of
  unheard-of

  adjective

  that was never heard of; unknown.
• unheard of
  unheard of

  Very unusual, extraordinary, as in It's unheard of to have all one's money refunded two years after the purchase. This expression alludes to a circumstance so unusual that it has never been heard of. [Late 1500s]

unheard-of

American  

[uhn-hurd-uhv, -ov, -uhv] / ʌnˈhɜrdˌʌv, -ˌɒv, -əv /

adjective

1. that was never heard of; unknown.

   an unheard-of artist.

2. such as was never known before; unprecedented.

   an unheard-of salary.

3. shocking or outrageous.

   unheard-of conduct.

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unheard-of British  

adjective

1. previously unknown

   an unheard-of actress

2. without precedent

   an unheard-of treatment

3. highly offensive

   unheard-of behaviour

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unheard of Idioms  

1. Very unusual, extraordinary, as in It's unheard of to have all one's money refunded two years after the purchase. This expression alludes to a circumstance so unusual that it has never been heard of. [Late 1500s]

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Etymology

Origin of unheard-of

First recorded in 1585–95

Example Sentences

"That's an unheard-of pace of innovation in developing complex structural alloys."

From Science Daily • Mar. 10, 2026

“Imagine that the tools of chemistry could be used to create entirely new materials with unheard-of properties,” Heiner Linke, chair of the Nobel Committee for Chemistry, said Wednesday.

From The Wall Street Journal • Oct. 8, 2025

His thesis at the Navy Academy was in the unheard-of topic of liquid-fuel engines.

From BBC • Aug. 9, 2025

And it has highlighted the challenges of preparing for unheard-of weather events, like a hurricane in the mountains.

From Slate • Nov. 2, 2024

Maybe that was why they’d adopted the unheard-of measure of ‘owning’ prey.

From "Wolf Brother" by Michelle Paver

Related Words

• exceptional
• inconceivable
• little-known
• unbelievable
• undiscovered
• unprecedented