Acidulate, v. t. [imp. & p. p. Acidulated; p. pr. & vb. n. Acidulating.] — Webster enters it under “acidulate”
Etymology: [Cf. F. aciduler. See Acidulous.]
To make sour or acid in a moderate degree; to sour somewhat. Arbuthnot.
Shades of meaning
Fernald has no entry of its own for acidulated; he lists it under bitter.
He lists it without comment; the entries above explain its neighbors.