1A mainly black swan with white flight feathers which is common in Australia and Tasmania and has been introduced elsewhere.
Cygnus atratus, family Anatidae
2An unpredictable or unforeseen event, typically one with extreme consequences.‘the bank industry's vulnerability to black swans’
- ‘black swan events always look eminently predictable in hindsight, yet no one ever predicts them’
3Something extremely rare.
- ‘husbands without faults, if such black swans there be’