black swan

Meaning

1. Cygnus atratus, a swan with black plumage and a red bill which is endemic to Australia.
2. (figuratively) Something believed impossible or not to exist, especially if an example is subsequently found; also, something extremely rare; a rara avis.
3. (also, attributive, figuratively, specifically) A rare and hard-to-predict event with major consequences.

Synonyms

Cygnus atratus

rarity

Translations

cygne noir

cigno nero

Trauerschwan

Schwarzschwan

Cygnus atratus

cisne negro

schwarzer Schwan

zwarte zwaan

Anas atrata

Chenopis atratus

Zwarte zwaan

Cisne-negro

cisne-negro

Pronounced as (IPA)

/blæk ˈswɒn/

Etymology

Inherited from Middle English: blak swan

In summary

From Middle English blak swan, calqued from a Latin quotation from Satire VI (written late 1st century – early 2nd century B.C.E.) of the Roman poet Juvenal: “Rara avis in terris, nigroque simillima cygno [a bird as rare upon the earth as a black swan]!”. Equivalent to black + swan.
Sense 2.1 (“something believed impossible or not to exist”) is from the fact that all swans were thought to have white plumage until black swans were discovered in Australia in the 17th century by Dutch explorers. Sense 2.2 (“rare and hard-to-predict event”) was popularized by the Lebanese-American author Nassim Nicholas Taleb (born 1960) in his book The Black Swan: The Impact of the Highly Improbable (2007): see the quotation.