Acidulous, a.
Etymology: [L. acidulus, dim. of acidus. See Acid.]
Slightly sour; sub-acid; sourish; as, an acidulous tincture. E. Burke. Acidulous mineral waters, such as contain carbonic anhydride.
Shades of meaning
Fernald has no entry of its own for acidulous; he lists it under bitter.
He lists it without comment; the entries above explain its neighbors.