#1 sour v. [turn, ferment, work] go sour or spoil; "The milk has soured"; "The wine worked"; "The cream has turned--we have to throw it out". wn
#2 sour s. [rancid] smelling of fermentation or staleness. wn
#3 sour v. [acidify, acidulate, acetify] make sour or more sour. wn
#4 sour n. a cocktail made of a liquor (especially whiskey or gin) mixed with lemon or lime juice and sugar. wn
#5 sour n. [sourness, tartness] the taste experience when vinegar or lemon juice is taken into the mouth. wn
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