If something is sour, it has a tangy or sharp flavor, like a lemon. Your brother may love the taste of limes, while they're way too sour for you.

Sometimes this adjective is used to describe a fermented odor (the way milk smells when it goes bad), or a wrong note in music, or even a terrible mood: "Mom was acting so sour that I didn't even ask her if we could have pizza for dinner." Sour comes from the Old English sur, "sour, tart, or fermented."

Definitions of sour
  1. adjective
    one of the four basic taste sensations; like the taste of vinegar or lemons
    pleasing to the sense of taste
  2. adjective
    having a sharp biting taste
    (of liquor) having a low residual sugar content because of decomposition of sugar during fermentation
    acerb, acerbic, astringent
    sour or bitter in taste
    acetose, acetous, vinegarish, vinegary
    tasting or smelling like vinegar
    acid, acidic, acidulent, acidulous
    being sour to the taste
    lemonlike, lemony, sourish, tangy, tart
    tasting sour like a lemon
    slightly sour to the taste
    having turned bad
    pleasing to the sense of taste
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    having or denoting the characteristic taste of sugar
    containing sugar
    (used of wines) having a high residual sugar content
    cloying, saccharine, syrupy, treacly
    overly sweet
    somewhat sweet
    pleasing to the sense of taste
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  3. noun
    the property of being acidic
    synonyms: acidity, sourness
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    acerbity, tartness
    a sharp sour taste
    vinegariness, vinegarishness
    a sourness resembling that of vinegar
    type of:
    taste property
    a property appreciated via the sense of taste
  4. noun
    the taste experience when vinegar or lemon juice is taken into the mouth
    synonyms: sourness, tartness
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    acidity, acidulousness
    the taste experience when something acidic is taken into the mouth
    type of:
    gustatory perception, gustatory sensation, taste, taste perception, taste sensation
    the sensation that results when taste buds in the tongue and throat convey information about the chemical composition of a soluble stimulus
  5. noun
    a cocktail made of a liquor (especially whiskey or gin) mixed with lemon or lime juice and sugar
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    whiskey sour, whisky sour
    a sour made with whiskey
    type of:
    a short mixed drink
  6. verb
    make sour or more sour
    synonyms: acetify, acidify, acidulate
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    dulcify, dulcorate, edulcorate, sweeten
    make sweeter in taste
    type of:
    change taste
    alter the flavor of
  7. adjective
    in an unpalatable state
    sour milk”
    synonyms: off, turned
    having turned bad
  8. adjective
    smelling of fermentation or staleness
    synonyms: rancid
    ill-smelling, malodorous, malodourous, stinky, unpleasant-smelling
    having an unpleasant smell
  9. verb
    go sour or spoil
    “The milk has soured
    synonyms: ferment, turn, work
    ferment, work
    cause to undergo fermentation
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    type of:
    change state, turn
    undergo a transformation or a change of position or action
  10. adjective
    inaccurate in pitch
    synonyms: false, off-key
    inharmonious, unharmonious
    not in harmony
  11. adjective
    showing a brooding ill humor
    “a sour temper”
    synonyms: dark, dour, glowering, glum, moody, morose, saturnine, sullen
    having an irritable and unpleasant disposition
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