unheard-of

[uhn-hurd-uhv, -ov, -uh v] /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.
Origin
1585-95
British Dictionary definitions for unheard of

unheard-of

adjective
1.
previously unknown: an unheard-of actress
2.
without precedent: an unheard-of treatment
3.
highly offensive: unheard-of behaviour
Idioms and Phrases with 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 ]