[uhn-hurd-uhv, -ov, -uh
v] 
| 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. |
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]