eight

behind the eight ball at a disadvantage; baffled. North American

☞ The black ball is numbered eight in a variety of the game of pool known as eight-ball pool.

one over the eight slightly drunk. British informal

☞ The idea behind this idiom is that a drinker can reasonably be expected to consume eight glasses of beer without becoming drunk. The expression was originally armed forces' slang from the early 20th century.