<p><strong>Adjective</strong></p><ul><li>having an acid taste, resembling that of vinegar, lemon juice, etc.; tart.</li><li>rendered acid or affected by fermentation; fermented.</li><li>producing the one of the four basic taste sensations that is not bitter, salt, or sweet.</li><li>characteristic of something fermented: a sour smell.</li><li>distasteful or disagreeable; unpleasant.</li><li>harsh in spirit or temper; acrimonious; disagreeable; peevish.</li><li>(of soil) having excessive acidity.</li><li>(of gasoline or the like) contaminated by sulfur compounds.</li><li>off-pitch; badly produced: a sour note.</li></ul><p><strong>Noun</strong></p><ul><li>something that is sour.</li><li>any of various cocktails consisting typically of whiskey or gin with lemon or lime juice and sugar and sometimes soda water, often garnished with a slice of orange, a maraschino cherry, or both.</li><li>any of various beers with a particularly acidic or tart taste, made so by acid-producing bacteria and yeast in the brew: Sours are a good choice to go with deep-fried bar food.</li><li>an acid or an acidic substance used in laundering and bleaching to neutralize alkalis and to decompose residual soap or bleach.</li></ul><p><strong>Verb (used without object)</strong></p><ul><li>to become sour, rancid, mildewed, etc.; spoil: Milk sours quickly in warm weather.</li><li>to become unpleasant or strained; worsen; deteriorate: Relations between the two countries have soured.</li><li>to become bitter, disillusioned, or disinterested: I guess I soured when I learned he was married.</li></ul><p><strong>Verb (used with object)</strong></p><ul><li>to make sour; cause sourness in: What do they use to sour the mash?</li><li>to cause spoilage in; rot: Defective cartons soured the apples.</li><li>to make bitter, disillusioned, or disagreeable: One misadventure needn't have soured him.</li></ul>