The Collaborative International Dictionary of English v.0.48:

Sour \Sour\, v. t. [AS. s?rian to sour, to become sour.]
   1. To cause to become sour; to cause to turn from sweet to
      sour; as, exposure to the air sours many substances.
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            So the sun's heat, with different powers,
            Ripens the grape, the liquor sours.   --Swift.
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   2. To make cold and unproductive, as soil. --Mortimer.
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   3. To make unhappy, uneasy, or less agreeable.
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            To sour your happiness I must report,
            The queen is dead.                    --Shak.
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   4. To cause or permit to become harsh or unkindly. "Souring
      his cheeks." --Shak.
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            Pride had not sour'd nor wrath debased my heart.
                                                  --Harte.
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   5. To macerate, and render fit for plaster or mortar; as, to
      sour lime for business purposes.
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The Collaborative International Dictionary of English v.0.48:

Sour \Sour\, a. [Compar. Sourer; superl. Sourest.] [OE.
   sour, sur, AS. s?r; akin to D. zuur, G. sauer, OHG. s?r,
   Icel. s?rr, Sw. sur, Dan. suur, Lith. suras salt, Russ.
   surovui harsh, rough. Cf. Sorrel, the plant.]
   1. Having an acid or sharp, biting taste, like vinegar, and
      the juices of most unripe fruits; acid; tart.
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            All sour things, as vinegar, provoke appetite.
                                                  --Bacon.
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   2. Changed, as by keeping, so as to be acid, rancid, or
      musty, turned.
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   3. Disagreeable; unpleasant; hence; cross; crabbed; peevish;
      morose; as, a man of a sour temper; a sour reply. "A sour
      countenance." --Swift.
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            He was a scholar . . .
            Lofty and sour to them that loved him not,
            But to those men that sought him sweet as summer.
                                                  --Shak.
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   4. Afflictive; painful. "Sour adversity." --Shak.
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   5. Cold and unproductive; as, sour land; a sour marsh.
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   Sour dock (Bot.), sorrel.

   Sour gourd (Bot.), the gourdlike fruit Adansonia
      Gregorii, and Adansonia digitata; also, either of the
      trees bearing this fruit. See Adansonia.

   Sour grapes. See under Grape.

   Sour gum (Bot.) See Turelo.

   Sour plum (Bot.), the edible acid fruit of an Australian
      tree (Owenia venosa); also, the tree itself, which
      furnished a hard reddish wood used by wheelwrights.
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   Syn: Acid; sharp; tart; acetous; acetose; harsh; acrimonious;
        crabbed; currish; peevish.
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The Collaborative International Dictionary of English v.0.48:

Sour \Sour\, n.
   A sour or acid substance; whatever produces a painful effect.
   --Spenser.
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The Collaborative International Dictionary of English v.0.48:

Sour \Sour\, v. i. [imp. & p. p. Soured; p. pr. & vb. n.
   Souring.]
   To become sour; to turn from sweet to sour; as, milk soon
   sours in hot weather; a kind temper sometimes sours in
   adversity.
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         They keep out melancholy from the virtuous, and hinder
         the hatred of vice from souring into severity.
                                                  --Addison.
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WordNet (r) 3.0 (2006):

sour
    adj 1: smelling of fermentation or staleness [syn: sour,
           rancid]
    2: having a sharp biting taste [ant: sweet]
    3: one of the four basic taste sensations; like the taste of
       vinegar or lemons
    4: in an unpalatable state; "sour milk" [syn: off, sour,
       turned]
    5: inaccurate in pitch; "a false (or sour) note"; "her singing
       was off key" [syn: false, off-key, sour]
    6: showing a brooding ill humor; "a dark scowl"; "the
       proverbially dour New England Puritan"; "a glum, hopeless
       shrug"; "he sat in moody silence"; "a morose and unsociable
       manner"; "a saturnine, almost misanthropic young genius"-
       Bruce Bliven; "a sour temper"; "a sullen crowd" [syn: dark,
       dour, glowering, glum, moody, morose, saturnine,
       sour, sullen]
    n 1: a cocktail made of a liquor (especially whiskey or gin)
         mixed with lemon or lime juice and sugar
    2: the taste experience when vinegar or lemon juice is taken
       into the mouth [syn: sour, sourness, tartness]
    3: the property of being acidic [syn: sourness, sour,
       acidity]
    v 1: go sour or spoil; "The milk has soured"; "The wine worked";
         "The cream has turned--we have to throw it out" [syn:
         sour, turn, ferment, work]
    2: make sour or more sour [syn: sour, acidify, acidulate,
       acetify] [ant: dulcify, dulcorate, edulcorate,
       sweeten]

Moby Thesaurus II by Grady Ward, 1.0:

247 Moby Thesaurus words for "sour":
   abrupt, absonant, acerb, acerbate, acerbic, acerbity, acescency,
   acescent, acetify, acid, acidic, acidify, acidity, acidulant,
   acidulate, acidulated, acidulent, acidulous, acidulousness, acrid,
   acrimonious, aftertaste, agent provocateur, aggravate, amaroidal,
   amplify, annoy, asperous, astringent, atonal, augment, bad,
   bad-tempered, bilious, biting, bitter, bitter as gall, blown,
   bread-and-butter pickle, brusque, build up, cacophonous, caustic,
   chokecherry, choleric, churlish, coarse, crab, crab apple, crabbed,
   crabby, cracked, cranky, cross, crusty, curdle, curdled, curt,
   cutting, deepen, deteriorate, diaphonic, dill pickle, disagreeable,
   disconsonant, discontented, discordant, disenchant, disharmonic,
   disharmonious, dislikable, displeasing, dissonant, distasteful,
   dry, dryness, dyspeptic, edgy, embitter, embittered, enhance,
   enlarge, envenom, escharotic, exacerbate, exasperate, ferment,
   fermented, flat, flavor, frowy, gamy, gloomy, go bad, go off,
   gone off, grating, green, green apple, greenness, grouchy, gust,
   hard, harsh, heat up, heighten, high, hot up, hyperacidity,
   ill-natured, ill-tempered, immelodious, impatient, increase,
   inharmonic, inharmonious, intensify, irritate, irritating,
   jaundiced, keen, lemon, lime, magnify, make acute, make worse,
   mordant, morose, musicless, nasty, nonmelodious, nose-tickling,
   off, off-key, off-tone, out of pitch, out of tone, out of tune,
   palate, peeve, peevish, penetrating, petulant, pickle, pickled,
   piercing, piquant, poignant, provoke, pungency, pungent, rancid,
   rank, raucous, reechy, relish, rough, salt, sapidity, sapor, savor,
   savoriness, sec, severe, sharp, sharpen, shrill, smack, snappish,
   sour as vinegar, sour balls, sour cream, sour grapes, sour pickle,
   sour-tempered, sourdough, soured, sourish, sourishness, sourness,
   spoil, spoiled, spoilt, stale, stinging, stomach, strident, strong,
   subacidity, sullen, sweet, tainted, tang, tart, tartish,
   tartishness, tartness, taste, terrible, testy, thankless, tongue,
   tooth, trenchant, tuneless, turn, turn sour, turned, ugly,
   unalluring, unappealing, unappetizing, unattractive, undelectable,
   undelicious, undesirable, unengaging, unenjoyable, unharmonious,
   uninviting, unlikable, unmelodious, unmusical, unpalatable,
   unpleasant, unpleasing, unripe, unripeness, unsavory, unsweet,
   unsweetened, unsweetness, untasteful, untunable, untuned,
   untuneful, unwelcome, verjuice, vex, vinegar, vinegariness,
   vinegarish, vinegarishness, vinegary, vitriolic, worsen, yogurt