1. having a sharp, acidic taste like lemon or vinegar
2. having gone bad or spoiled
3. bad-tempered or unfriendly

1. to become or make acidic or spoiled
2. to become unpleasant or unfriendly

Examples

• The lemon was very sour.
• The milk had gone sour in the heat.
• He gave me a sour look when I arrived late.
• Their relationship began to sour after the argument.
• The cream will sour if left out too long.
• Her mood turned sour when she heard the news.