noun

1. SOUR, the property of being acidic
2. SOUR, the taste experience when vinegar or lemon juice is taken into the mouth
3. SOUR, a cocktail made of a liquor (especially whiskey or gin) mixed with lemon or lime juice and sugar

verb

1. SOUR, go sour or spoil
2. SOUR, make sour or more sour
3. SOUR, an alcoholic drink that has a sour taste
4. SOUR, to lose freshness and get an unpleasant taste or smell : to become sour
5. SOUR, to become unpleasant or unfriendly
6. SOUR, to make (someone or something) unpleasant or unfriendly

adjective

1. SOUR, smelling of fermentation or staleness
2. SOUR, showing a brooding ill humor
3. SOUR, inaccurate in pitch
4. SOUR, in an unpalatable state
5. SOUR, one of the four basic taste sensations; like the taste of vinegar or lemons

adjective

1. SOUR, having a sharp biting taste

1. The milk had turned sour.
2. He made a sour face.
3. Her disposition has soured in recent years.
4. Jealousy has soured their relationship.
5. His experiences have soured him.