I found the phrase “keep the black dog at bay” in an article titled “ Ways to Beat the Winter Blues” in Time magazine November 14 issue. The phrase comes up at the end of the following statement:
“As the days get shorter and winter closes in, many people feel like hibernating. We start sleeping more, eating more and avoiding social contact. The effects can be particularly oppressive for people with depression, many of whom feel escalating dread as the end of daylight saving time approaches. Here are eight ways to keep the black dog at bay after you turn back the clocks.”
I checked definition of “keep the black dog at bay” on several online dictionaries. None of Cambridge, Oxford, Merriam-Webster, and even Urban dictionary registers this phrase.
What does "keep the black dog at bay" mean? I wonder whether “black dog” is used as a pun with “winter blue” in the headline. Is “keep the black dog at bay” a well-established idiom?