Definition of sour

The word "sour" has its roots in Old English and dates back to around the 9th century. Initially, it meant "to decay" or "to deteriorate". This sense of decay likely came from the observation that fermenting foods and drinks would become sour-tasting as they broke down. Over time, the word "sour" expanded to describe not just the taste, but also the emotional state of being unhappy, irritable, or disappointed. This emotional sense of "sour" emerged in the 14th century, possibly due to the association between the bitter or unpleasant taste of spoiled food and the negative emotions it evokes. Today, "sour" can refer to both a physical sensation (the taste of lemons or vinegar) and an emotional state (feeling bitter or unpleasantly challenged).