black swan

American  

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.

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black swan British  

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

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Etymology

Origin of black swan

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

Example Sentences

In the words of one central-bank manager, he quoted, the precious metal is the “ultimate protection against black swan tail risk events”.

From MarketWatch

He doesn’t discount the possibility of a “black swan”-type event in the near future.

From MarketWatch

That implies that barring a black swan event, the current easing cycle is close to done.

From The Wall Street Journal

But whether Eve’s inner black swan will win out over her white one is never in question.

From Los Angeles Times

A “black swan” moment — a tipping point for justice — is approaching.

From Los Angeles Times