The term "hair of the dog" is a colloquial expression used to refer to a drink of alcohol consumed to alleviate the symptoms of a hangover. It is thought to have originated from the belief that the best cure for a dog bite was to apply the hair of the dog that bit you to the wound.
The practice of drinking alcohol to cure a hangover has been around for centuries. In the 16th century, the English physician John Caius recommended drinking a glass of wine or ale to treat hangover symptoms. Today, many people swear by the hair of the dog as a hangover cure, while others believe it only prolongs the hangover.