a cocktail made of a liquor (especially whiskey or gin) mixed with lemon or lime juice and sugar
"He ordered a sour to go along with his steak dinner."
The sensation of a sour taste.
"The lemon made my mouth water with its sharp, sour taste."
In plain English: A sour is an unpleasant feeling of regret or disappointment that happens when you realize something bad has already occurred and cannot be changed.
"The sour in this lemon was so intense that I made my jaw hurt just biting into it."
To make sour.
"The spoiled milk began to sour when left out in the sun."
having a sharp biting taste
"The lemon had such a sour flavor that it made my teeth ache from its sharp, biting taste."
one of the four basic taste sensations; like the taste of vinegar or lemons
"The lemon juice made the punch taste distinctly sour."
showing a brooding ill humor
"a dark scowl"
"the proverbially dour New England Puritan"
"a glum, hopeless shrug"
"he sat in moody silence"
"a morose and unsociable manner"
"a saturnine, almost misanthropic young genius"
"a sour temper"
"a sullen crowd"
Having an acidic, sharp or tangy taste.
"The lemon was so sour that it made my teeth ache immediately after I took a bite."
In plain English: Sour describes something that tastes sharp and unpleasant, like an unripe lemon.
"The milk has gone sour, so we cannot drink it anymore."
The word "sour" comes directly from the same root in both Middle and Old English. It has been used to describe a sharp or acidic taste since ancient times, traveling through Germanic languages all the way back to Proto-Indo-European origins without changing its fundamental meaning.