Definition of "unheard-of"

unheard-of

adjective
comparative more unheard-of, superlative most unheard-of
1. Previously unknown; unprecedented.
  Quotations
  He was […] none of your unconscionable blades, requiring impossible chops, and taking unheard-of pickles for granted.
  1841 February–November, Charles Dickens, “Barnaby Rudge”, in Master Humphrey’s Clock, volume II, London: Chapman & Hall, […], chapter 10, page 289
  Starvation in the uplands was not an unheard-of thing; […]
  1912 January, Zane Grey, “Silver Spruce and Aspens”, in Riders of the Purple Sage […], New York, N.Y., London: Harper & Brothers Publishers, page 114
  Prohibition produced the immense and previously unheard-of wealth that launched truly organized crime in America.
  2004, Peter Bondanella, chapter 4, in Hollywood Italians: Dagos, Palookas, Romeos, Wise Guys, and Sopranos, page 175
2. Unknown or known to only few people.