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.
I believe that the black dog is a Newfoundland dog,here is a picture: http://rlv.zcache.com/newfoundland_dog_p... I also think that the brown dog is an Irish Wolfhound,here is a picture of that too: http://www.dkimages.com/discover/preview... M@rc0$ Â· 6 years ago. Thumbs up. 0.