What made you want to look up xenial? Please tell us where you read or heard it (including the quote, if possible).
Black dog is an oft-used phrase to mean depression. Here's a link that attributes the phrase to Winston Churchill, but I suspect he didn't invent it. I like the way they described it though: Black Dog was Churchill's name for his depression, and as is true with all metaphors, it speaks volumes.
What breeds of dog have a black tongue? Because Chows are the dogs most known as having black or black-spotted tongues, some mistakenly assume that a dog with a black tongue is a Chow or at least part Chow. In realiâ¦ty, there are many other breeds of dog that may have black spots on their tongue or gums.