- 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.
- previously unknownan unheard-of actress
- without precedentan unheard-of treatment
- highly offensiveunheard-of behaviour
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]