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

If a black swan is a metaphor for rare, unpredictable market events, then it’s only the energy market that is seeing black-swan style price dynamics, they say.

From MarketWatch • Mar. 18, 2026

Although they may not come to pass, there are plenty of potential black swan events that could be lurking in the back half of the 2020s.

From Barron's • Feb. 26, 2026

He called the Eaton fire “a black swan event” — one of “low probability, but high consequence.”

From Los Angeles Times • Dec. 17, 2025

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

From The Wall Street Journal • Oct. 10, 2025

The serving men brought out a heron stuffed with figs, veal cutlets blanched with almond milk, creamed herring, candied onions, foul-smelling cheeses, plates of snails and sweetbreads, and a black swan in her plumage.

From "A Dance with Dragons" by George R. R. Martin