adj. 1 acid, acidic, tart, vinegary, lemony, acidulous or acidulent, acidulated, acescent, acerbic This apple has a pleasant, slightly sour taste Do you like sour dill pickles? 2 turned, bad, (gone) off, fermented, curdled, rancid, spoilt or spoiled If the food is sour, throw it away 3 disagreeable, unpleasant, distasteful, bad, nasty, bitter, terrible The poor service and facilities made the entire holiday a very sour experience 4 acrimonious, bitter, embittered, unpleasant, churlish, ill-natured, ill-tempered, bad-tempered, crusty, curmudgeonly, crabbed, crabby, grouchy, cross, cranky, testy, petulant, impatient, abrupt, nasty, curt, caustic, brusque, peevish, snappish, edgy, sullen, morose, gloomy, discontented The waitress's sour expression matched her sour disposition
v. 5 turn, spoil, curdle, go bad or off, ferment Milk sours quickly in this climate if you don't refrigerate it 6 embitter, acerbate, disenchant, exasperate, vex, Colloq peeve Being forced to practise for hours when a child was what soured my enjoyment of playing the piano