black swan

noun

1. an Australian swan, Cygnus atratus, having mostly black plumage and a red bill.
2. an occurrence or phenomenon that comes as a surprise because it was not predicted or was hard to predict (often used attributively):

   a disastrous black-swan event that only appeared obvious in hindsight.

black swan

noun

1. a large Australian swan, Cygnus atratus , that has a black plumage and red bill
2. a phenomenon that occurs even though it had been thought to be impossible

Word History and Origins

Origin of black swan¹

black swan ( def 2 ) from the belief that all swans were white, before the first sighting of Australian black swans

Word History and Origins

Origin of black swan¹

sense 2 from the fact all swans were thought to be white until black swans were discovered in Australia

Example Sentences

But experts have told the BBC that this was likely a "black swan" occurrence of freak weather - and that no-one is necessarily at fault.

From BBC

This seems puzzling on its face since Biden’s impending bailout had been the subject of chatter for months and may have been the best-advertised “black swan” event in history.

From Salon

A groggy black swan emerged from the X-ray room, head swaying on its long neck.

From New York Times

Am I concerned about Mike Flynn ginning up violence and promising black swan events as he traipses around the countryside of wing states with his merry band of grifters selling Kremlin talking points as patriotism?

From Salon

And I'm saying, barring another black swan event, he will be President again.

From Salon