one over the eight
have one over (the) eight
To have enough alcoholic drinks to be thoroughly inebriated. Primarily heard in UK. I was composed and in control of myself for most of the evening, but somewhere around midnight, I had one over the eight and started making a show of myself. It seems like Jenny makes a point of having one over eight every time she goes out on the weekend.
one over the eightslightly 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.