Noun
(euphemistic) depression, melancholy
Used other than figuratively or idiomatically: see black, dog.
Source: en.wiktionary.orgAlways armed and now accompanied by a big black dog he named “Corvo” (Crow), “he looked more like a swordsman than a painter,” as one early biographer wrote. Source: Internet
From the black children's white cat, to the white children's black dog, the busy work of the movers, and the neighbors peering out their windows in the background, each detail of the illustration creates an atmosphere of tension. Source: Internet
During the notorious Salem witch trials in New England in 1692–93, one of those on trial was accused of being able turn into a "black thing with a blue cap," and others of having familiars in the form of a black dog, a black cat and a black bird. Source: Internet
As William Rees-Mogg has stated, "In his own life, he had to suffer the 'black dog' of depression. Source: Internet
Speculation exists that the face is actually that of a black dog. Source: Internet
The spirit of the dead, camaquen, would need to follow a long road and during the trip the assistance of a black dog that could see in the dark was required. Source: Internet