Overproof

Leeward Island Rums are but seldom brought to this country at a higher rate of strength, than eight or ten per cent. overproof.

Source: wiktionary

In overproof spirit, the per centage overproof always represents the quantity of water it will take to reduce it to proof. By adding its per centage overproof to 100, we obtain a number, which, multiplied by any number of gallons, and divided by 100, will give the exact number of proof gallons which is contained in the given quantity of spirit of that strength.

Source: wiktionary

Now the rum, as has been said, was criminally overproof, and they had had no intoxicants for a long time. And so a couple of stiff drinks produced a beautiful and generous expansion of soul. The mean cabin became larger, the fire warmer and more cheerful, and life generally of a more roseate hue. They began to feel the prodigal Thanksgiving spirit, and to regret their limited opportunities for satisfying it.

Source: wiktionary

The Zombie, created by Don the Beachcomber, first appeared in 1934 as a hangover cure. […] The rule of no more than two per person was in place from the moment of its conception, due to the sheer amount of booze in the drink, not to mention the overproof rum float on top, and this still remains in place in many venues to this day.

Source: wiktionary