Cygnus atratus, an Australian swan whose feathers are black. / (figuratively) Something believed impossible or not to exist, of which an example is subsequently found.

A tree of the species Betula lenta, with a dark bark resembling a cherry tree's and an aromatic bark and sap used for birch beer.

A tinamou, Tinamus osgoodi.

(medicine, historical) A pandemic outbreak of bubonic plague throughout Europe and most of Asia in the 14th century that killed nearly half the population of Europe and Asia.

A practice such as witchcraft, sorcery, necromancy, or black magic. / (figuratively, by extension) A process that is mysterious or difficult to master.

One of the four humours of ancient and mediaeval physiology, that was believed to be secreted by the kidneys and spleen and to cause melancholy and sadness when present in excess.

a member of an African-American religious movement with political overtones; either of the Nation of Islam or the American Muslim Mission (open to all races)

(US, slang, law enforcement) A police patrol car. / (US, slang, by extension) The police, a police officer or the clothing they wear.

Alternative form of black-and-white (of an image, a video, etc: in black, white, and perhaps shades of grey, rather than in colour)

(informal, aviation) A flight recorder; the brightly colored cockpit voice recorders and flight data recorders in an aircraft designed to aid in determining the cause of an accident.