Sour, acid, acidulous, tart, dry mean having a taste devoid of sweetness.
All but dry suggest the taste of lemons, vinegar, or of most unripe fruits.
Sour and acid are often interchangeable, but sour is more likely to be chosen to describe something that through fermentation has lost its natural sweet or neutral taste or, sometimes, smell and the term may additionally suggest a spoiled or rancid state.
Acid, on the other hand, is appropriately used to describe something having a sharp sweetless taste in its natural state usually due to the presence of chemical acids.
Acidulous and tart are applied, as a rule, to things which may be described as acid, acidulous implying a modest degree of acidity and tart, a sharp but often agreeable acidulousness or, sometimes, acidity.
Dry is usually applied to wines which, although without any sweetness, are bland and therefore neither definitely acid nor definitely sour. In their extended senses sour applies especially to what is crabbed or morose and acidulous and tart to what is characterized by asperity, pungency, or sharpness.
Acid, partly by allusion to the corrosive powers of some acids, is likely to describe what is biting or caustic while dry may suggest matter-of-fact impersonal presentation of what is humorous, ironic, or sarcastic.