"sub-acidic, slightly sour" (of cream of tartar, oranges, etc.), 1766, also used figuratively for "sour-tempered;" from Latin acidulus "slightly sour," a diminutive of acidus (see acid (adj.)).

"make somewhat sour, flavor with an acid," 1704 (implied in acidulated), from Latin acidulus "slightly sour" (see acidulous) + -ate (2). Related: Acidulating; acidulent.