a small quantity of alcohol taken as a remedy for a hangover – informal
The full form of this phrase is hair of the dog that bit you. Hair from a rabid dog was at one time thought to be a remedy against the effects of its bite. In this expression, the recommended cure for a hangover is a small amount of the cause of the problem.
1987 - Bruce Allen Powe - The Ice Eaters - Murray, still feeling the effects of the previous evening, had suggested they go into a bar because he needed a hair of the dog.
keep your hair on
used to urge someone not to panic or lose their temper - British informal
let your hair down
behave wildly or uninhibitedly – informal
make his hair stand on end
alarm or horrify someone
neither hide nor hair of him
not the slightest trace of someone
not turn a hair
remain apparently unmoved or unaffected
put hairs on your chest
(of alcoholic drink) revive your strength – informal
make small and overfine distinctions
This expression was first recorded in the late 17th century. Split straws, dating from the 19th century, is a less common version.