The Cusith, or Cu Sìth is an enormous fairy hound of the Scottish Highlands.
Cu Sìth literally means 'fairy dog.'
Roughly the size of a cow or large calf, the Cu Sìth was said to be dark green in color with shaggy fur and a long braided or curled tail and glowing or flaming eyes. Supernatural dogs in Celtic mythos are usually completely black, or white with red ears. The Cu Sìth's coloration is therefore highly unusual, although it may be derived from the green color often worn by Celtic fairies. In Irish mythology the Cu Sith was said to be an immense, coal black hound with glowing or burning eyes.
The Cu Sith was feared as a harbinger of death and would appear to bear away the soul of a person to the afterlife.
Legend has it that the creature was capable of hunting silently, but would occasionally let out three terrifying barks that could be heard for long distances, including by ships at sea. This was said to be a warning to farmers to lock up their women, lest the beast abduct them and take them to a fairy mound (Scottish Gaelic, sìthean ) to supply milk for fairy (daoine-sìth) children. If a person was pursued by the Cu Sith, their only chance to escape the creature was to reach home before it barked three times. If this happened, the victim had no chance of getting away.