sour wine: the cheap, watered-down vinegar-wine that ordinary working people and Roman soldiers drank to quench thirst.
This word names a real drink, not the harsh condiment we call vinegar today. In the ancient world wine that had gone sour, thinned with water, was the everyday beverage of soldiers, sailors, and the laboring poor. It was cheap, plentiful, and actually quenched thirst better than plain water on a hot day. Romans called this ration drink posca, and Greek had no separate word for it, so they used this one.
The word and its meaning sit on a sliding scale. The same liquid could be called wine when fresh and sour wine once it aged, so the line between them was blurry. In its sharpest form it was the biting vinegar used to clean wounds or to torment, but in the Bible it almost always means the mild, drinkable kind. That ordinary, unremarkable quality is exactly what makes it striking in the Gospels.
Every New Testament use falls at the crucifixion. The soldiers on execution duty had a jar of this drink with them because they were drinking it themselves through the long hours, and one of them lifted a soaked sponge to Jesus on the cross. Knowing it was a common refreshment, not a punishing draft, is what opens up the harder question the Gospel writers raise: was the offer a small kindness or a final taunt?