sour

Etymology

From Middle English sour, from Old English sūr (“sour”), from Proto-West Germanic *sūr, from Proto-Germanic *sūraz (“sour”), from Proto-Indo-European *súHros (“sour”). Cognate with West Frisian soer, Dutch zuur (“sour”), Low German suur, German sauer (“sour”), Danish, Swedish and Norwegian sur, French sur (“sour”), Faroese súrur (“sour”), Icelandic súr (“sour, bitter”), Polish ser (“cheese”), Czech sýr (“cheese”), Slovak syr (“cheese”), Russian сырой (syroj, “raw”), Ukrainian сири́й (syrýj, “raw”), Old Church Slavonic сꙑръ (syrŭ, “moist, cheese”).

adj

1. Having an acidic, sharp or tangy taste.
   Lemons have a sour taste.
   A few types of molecules get sensed by receptors on the tongue. Protons coming off of acids ping receptors for "sour." Sugars get received as "sweet." Bitter, salty, and the proteinaceous flavor umami all set off their own neural cascades. May 16 2018, Adam Rogers, “The Fundamental Nihilism of Yanny vs. Laurel”, in Wired
2. Made rancid by fermentation, etc.
   Don't drink that milk; it's turned sour.
3. Tasting or smelling rancid.
   His sour breath makes it unpleasing to talk to him.
4. (of a person's character) Peevish or bad-tempered.
   He gave me a sour look.
5. (of soil) Excessively acidic and thus infertile.
   sour land
   a sour marsh
6. (of petroleum) Containing excess sulfur.
   sour gas smells like rotten eggs
7. Unfortunate or unfavorable.
   The result may not quite give the Wearsiders a sweet ending to what has been a sour week, following allegations of sexual assault and drug possession against defender Titus Bramble, but it does at least demonstrate that their spirit remains strong in the face of adversity. October 1, 2011, Phil Dawkes, “Sunderland 2 - 2 West Brom”, in BBC Sport
8. (music) Off-pitch, out of tune.
   Unlike what the name implies, there is nothing inherently wrong with a sour note: It is perfectly well-tuned note that would sound normal in another context (and which presumably would not sound sour to someone unfamiliar with tonal music). 2010, Aniruddh D. Patel, Music, Language, and the Brain, page 201

noun

1. The sensation of a sour taste.
2. A drink made with whiskey, lemon or lime juice and sugar.
3. (by extension) Any cocktail containing lemon or lime juice.
4. A sour or acid substance; whatever produces a painful effect.
5. The acidic solution used in souring fabric.

verb

1. (transitive) To make sour.
   Too much lemon juice will sour the recipe.
2. (intransitive) To become sour.
   So the sun's heat, with different powers, / Ripens the grape, the liquor sours. 1720, Jonathan Swift, To Stella, on transcribing my Poems
3. (transitive) To spoil or mar; to make disenchanted.
4. (intransitive) To become disenchanted.
   We broke up after our relationship soured.
5. (transitive) To make (soil) cold and unproductive.
   stagnant water , which tends to sour the soil 1832, Joseph Harrison, Sir Joseph Paxton, The Horticultural Register, page 396
6. To macerate (lime) and render it fit for plaster or mortar.
7. (transitive) To process (fabric) after bleaching, using hydrochloric acid or sulphuric acid to wash out the lime.