unheard-of

adjective

un·​heard-of ˌən-ˈhərd-ˌəv 

-ˌäv

: previously unknown

especially : unprecedented

moving at unheard-of speeds

Synonyms of unheard-of

• unprecedented
• novel
• strange
• unfamiliar
• new

Examples of unheard-of in a Sentence

houses selling at unheard-of prices

Recent Examples on the Web

The museum’s floor plan, especially its curved walls, presented previously unheard-of challenges for exhibiting artworks. — Wendy S. Walters, Architectural Digest, 12 Oct. 2026

An unheard-of benefit for this group of patients with this terrible disease. — Bryan C. Donohue, Baltimore Sun, 1 Sep. 2026

The band features an almost unheard-of 11 musicians, all among Ireland’s best in their musical specialties. — Dan Kelly august 30, Kansas City Star, 30 Aug. 2026

That is unheard-of with prolonged exposure, cognitive processing, and certainly SSRIs, the current standard-of-care options. — Anderson Cooper, CBS News, 16 Aug. 2026

Word History

First Known Use

1592, in the meaning defined above

Kids Definition

unheard-of

adjective

un·​heard-of

-ˌəv, 

-ˌäv

: previously unknown : unprecedented

moving at unheard-of speeds