adj

• (of a person's character) Hostile or unfriendly.
  "He gave me a sour look."
• (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)."

noun

• (by extension) Any cocktail containing lemon or lime juice.

verb

• (transitive) To make sour.
  "Too much lemon juice will sour the recipe."
• (intransitive) To become sour.
  "So the sun's heat, with different powers, / Ripens the grape, the liquor sours."
• (transitive) To spoil or mar; to make disenchanted.
  "To sour your happiness I must report, / The queen is dead."
• (intransitive) To become disenchanted.
  "We broke up after our relationship soured."