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.
exists and is an alternate of . 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 reality, there are many other breeds of dog that may have black spots on their tongue or gums. <br /><br /> The Chinese Shar-Pei (commonly referred to as the 'wrinkle dog') is another breed that is known to have a black tongue. Many breeds are known to have tongues or gums with black spots, prompting less knowledgeable owners to think they may have a dog that is of mixed parentage rather than a purebred.