Source : Webster's Revised Unabridged Dictionary (1913)

Acidulous \A*cid"u*lous\, a. [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.

Source : WordNet®

acidulous
     adj : tasting sour like acid [syn: {acidic}, {acidulent}]