1. a metaphorical representation of melancholy or depression:"I'm very happy, but the black dog is there, lurking around the corner"
Word Originmid 17th century (as a name for a small or counterfeit coin); the sense ‘melancholy or depression’ dates from the late 18th century, and may derive from folk tales of ghostly black dogs tormenting people. Winston Churchill used the expression when alluding to his periodic bouts of depression.
