Lewis & Short

ăcĭdŭlus, a, um, adj., dim. [acidus], a little sour, sourish, acidulous: sapor, Plin. 15, 15, 16, § 54: aqua, mineral water, id. 2, 103, 106, § 230; 31, 2, 5, § 9; so, fons, ib.