Definition of sour verb from the Oxford Advanced American Dictionary

     

    sour

     verb
    verb
    NAmE//ˈsaʊər//
     
    Verb Forms present simple I / you / we / they sour
     
    he / she / it sours
     
    past simple soured
     
    -ing form souring
     
     
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  1. 1[intransitive, transitive] (of relationships, attitudes, people, etc.) to change so that they become less pleasant or friendly than before; to make something do this The atmosphere at the house soured. sour something The disagreement over trade tariffs has soured relations between the two countries.
  2. 2[intransitive, transitive] sour (something) if milk sours or if something sours it, it becomes sour and has an unpleasant taste or smell
See the Oxford Advanced Learner's Dictionary entry: sour