Sour  —adj. 1 acid in taste or smell, esp. Because unripe or fermented. 2 morose; bitter. 3 (of a thing) unpleasant; distasteful. 4 (of the soil) dank. —v. Make or become sour.  go (or turn) sour 1 turn out badly. 2 lose one's keenness.  sourly adv. Sourness n. [old english]