previously unknown: an unheard-of actor without precedent: an unheard-of treatment highly offensive: unheard-of behaviour
WordReference Random House Learner's Dictionary of American English © 2025
unˈheard-ˌof,
adj.
WordReference Random House Unabridged Dictionary of American English © 2025- not seen before and not expected;
unprecedented:an unheard-of scientific advance. - outrageous;
shocking;
offensive:his unheard-of extravagance. - not previously known;
not famous:the debut of an unheard-of singer.
un•heard-of
(un hûrd′uv′, -ov′, -əv),USA pronunciation adj.
- that was never heard of;
unknown:an unheard-of artist. - such as was never known before;
unprecedented:an unheard-of salary. - shocking or outrageous:unheard-of conduct.
- 1585–95
Collins Concise English Dictionary © HarperCollins Publishers::
'unheard-of' also found in these entries (note: many are not synonyms or translations):